One should have a clear knowledge about the windows of MATLAB before starting to work on it. MATLAB includes a variety of different windows for displaying different types of information and performing special tasks. Each window can generally be opened/ closed, docked in the main window or popped out, and repositioned/resized depending on current needs/preferences. The Window menu helps you navigate between the currently open windows, while the Desktop menu lets you open new windows (which can also be done from the command window).

• Command Window: -The window where you type commands and non-graphic output is displayed. A `>>' prompt shows you the system is ready for input. The lower left hand corner of the main window also displays `Ready' or `Busy' when the system is waiting or calculating. Previous commands can be accessed using the up arrow to save typing and reduce errors. Typing a few characters restricts this function to commands beginning with those characters.

• Command History: - Records commands given that session and recent sessions. Can be used for reference or to copy and paste commands.

• Workspace: - Shows the all the variables that you have currently defined and some basic information about each one, including its dimensions, minimum, and maximum values. The icons at the top of the window allow you to perform various basic tasks on variables, creating, saving, deleting, plotting, etc. Double-clicking on a variable opens it in the Variable or Array Editor. All the variables that you've defined can be saved from one session to another using File>Save Workspace As (Ctrl-S). The extension for a workspace file is .mat.

• Current Directory: - The directory (folder) that MATLAB is currently working in. This is where anything you save will go by default, and it will also influence what files MATLAB can see. You won't be able to run a script that you saved that you saved in a different directory (unless you give the full directory path), but you can run one that's in a sub-directory. The Current Directory bar at the top centre of the main window lets you change directory in the usual fashion -- you can also use the UNIX commands cd and pwd to navigate through directories. The Current Directory window shows a list of all the files in the current directory.

• Editor:-  The window where you edit m-files --the files that hold scripts and functions that you've defined or are editing--  and includes most standard word-processing options and keyboard shortcuts. It can be opened by typing edit in the Command Window. Typing edit myfile will open myfile.m for editing. Multiple files are generally opened as tabs in the same editor window, but they can also be tiled for side by side comparison. Orange warnings and red errors appear as underlining and as bars in the margin. Hovering over them provides more information; clicking on the bar takes you to the relevant bit of text. Also remember that MATLAB runs the last saved version of a file, so you have to save before any changes take effect.

• Variable Editor or Array Editor: - Opens variables in an Excel-like format, and is useful for checking what data is in which column/row, checking that value is where you meant it to be, etc. Data can also be edited or created in this window. Double-clicking on a variable in the Workspace will open it for editing. Multiple variables are usually opened as tabs, but can also be tiled for side by side comparison.

• Figure Editor: - MATLAB opens figures in separate windows, which includes the ability to fine-tune the appearance of the plot, zoom, etc. You can also use the Data Cursor to extract values and save them to the Workspace. See the Help documentation for further detail. The figures can also be saved in a wide variety of formats -- it's usually a good idea to save them as an m-file (File>Generate M-file) if there's any chance at all you might want to modify the figure later and you haven't already saved the generating code in a m-file.

• MATLAB Help: - MATLAB’s help documentation is very good, and can tell you pretty much any-thing you need to know. Help>Product Help opens the Help Window, which works largely like a web browser, including forward and back buttons. Use the Contents tab for help oriented around a broad topic (most of what you need will be under the MATLAB heading, and then probably Getting Starting or Graphics) --Search or Index for more specific queries (e.g. interpolating values, polynomial fit, etc.). The `see also' at the end of each file is very useful if you haven't found quite the right thing. It can also suggest better ways of doing things. Typing help commandname in the Command Window will also bring up the help file for that command.

Written By,

Student @ VIT University

PWM

The Fading example demonstrates the use of analog output (PWM) to fade an LED. It is available in the File->Sketchbook->Examples->Analog menu of the Arduino software.

Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. The duration of "on time" is called the pulse width. To get varying analog values, you change, or modulate, that pulse width. If you repeat this on-off pattern fast enough with an LED for example, the result is as if the signal is a steady voltage between 0 and 5v controlling the brightness of the LED.

In the graphic below, the green lines represent a regular time period. This duration or period is the inverse of the PWM frequency. In other words, with Arduino's PWM frequency at about 500Hz, the green lines would measure 2 milliseconds each. A call to analogWrite() is on a scale of 0 - 255, such that analogWrite(255) requests a 100% duty cycle (always on), and analogWrite(127) is a 50% duty cycle (on half the time) for example.

Once you get this example running, grab your arduino and shake it back and forth. What you are doing here is essentially mapping time across the space. To our eyes, the movement blurs each LED blink into a line. As the LED fades in and out, those little lines will grow and shrink in length. Now you are seeing the pulse width.

analogWrite()

Description

Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to analogWrite(), the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() on the same pin). The frequency of the PWM signal is approximately 490 Hz.
On most Arduino boards (those with the ATmega168 or ATmega328), this function works on pins 3, 5, 6, 9, 10, and 11. On the Arduino Mega, it works on pins 2 through 13. Older Arduino boards with an ATmega8 only support analogWrite() on pins 9, 10, and 11.
The Arduino Due supports analogWrite() on pins 2 through 13, plus pins DAC0 and DAC1. Unlike the PWM pins, DAC0 and DAC1 are Digital to Analog converters, and act as true analog outputs.
You do not need to call pinMode() to set the pin as an output before calling analogWrite().
The analogWrite function has nothing to do with the analog pins or the analogRead function.

Syntax

analogWrite(pin, value)

Parameters

pin: the pin to write to.
value: the duty cycle: between 0 (always off) and 255 (always on).

Returns

nothing

Notes and Known Issues

The PWM outputs generated on pins 5 and 6 will have higher-than-expected duty cycles. This is because of interactions with the millis() and delay() functions, which share the same internal timer used to generate those PWM outputs. This will be noticed mostly on low duty-cycle settings (e.g 0 - 10) and may result in a value of 0 not fully turning off the output on pins 5 and 6.

Example

Sets the output to the LED proportional to the value read from the potentiometer.

 



int ledPin = 9;      // LED connected to digital pin 9

int analogPin = 3;   // potentiometer connected to analog pin 3

int val = 0;         // variable to store the read value



void setup()

{

  pinMode(ledPin, OUTPUT);   // sets the pin as output

}



void loop()

{

  val = analogRead(analogPin);   // read the input pin

  analogWrite(ledPin, val / 4);  // analogRead values go from 0 to 1023, analogWrite values from 0 to 255

}

analogRead()

Description

Reads the value from the specified analog pin. The Arduino board contains a 6 channel (8 channels on the Mini and Nano, 16 on the Mega), 10-bit analog to digital converter. This means that it will map input voltages between 0 and 5 volts into integer values between 0 and 1023. This yields a resolution between readings of: 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit. The input range and resolution can be changed using analogReference().
It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.

Syntax

analogRead(pin)

Parameters

pin: the number of the analog input pin to read from (0 to 5 on most boards, 0 to 7 on the Mini and Nano, 0 to 15 on the Mega)

Returns

int (0 to 1023)

Note

If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate based on a number of factors (e.g. the values of the other analog inputs, how close your hand is to the board, etc.).

Example

 
int analogPin = 3;     // potentiometer wiper (middle terminal) connected to analog pin 3
                       // outside leads to ground and +5V
int val = 0;           // variable to store the value read

void setup()
{
  Serial.begin(9600);          //  setup serial
}

void loop()
{
  val = analogRead(analogPin);    // read the input pin
  Serial.println(val);             // debug value
}

analogReference(type)

Description

Configures the reference voltage used for analog input (i.e. the value used as the top of the input range). The options are:

• DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
• INTERNAL: an built-in reference, equal to 1.1 volts on the ATmega168 or ATmega328 and 2.56 volts on the ATmega8 (not available on the Arduino Mega)
• INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
• INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)
• EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.

Parameters

type: which type of reference to use (DEFAULT, INTERNAL, INTERNAL1V1, INTERNAL2V56, or EXTERNAL).

Returns

None.

Note

After changing the analog reference, the first few readings from analogRead() may not be accurate.

Warning

Don't use anything less than 0V or more than 5V for external reference voltage on the AREF pin! If you're using an external reference on the AREF pin, you must set the analog reference to EXTERNAL before calling analogRead(). Otherwise, you will short together the active reference voltage (internally generated) and the AREF pin, possibly damaging the microcontroller on your Arduino board.
Alternatively, you can connect the external reference voltage to the AREF pin through a 5K resistor, allowing you to switch between external and internal reference voltages. Note that the resistor will alter the voltage that gets used as the reference because there is an internal 32K resistor on the AREF pin. The two act as a voltage divider, so, for example, 2.5V applied through the resistor will yield 2.5 * 32 / (32 + 5) = ~2.2V at the AREF pin.

digitalRead()

Description

Reads the value from a specified digital pin, either HIGH or LOW.

Syntax

digitalRead(pin)

Parameters

pin: the number of the digital pin you want to read (int)

Returns

HIGH or LOW

Example

 
int ledPin = 13; // LED connected to digital pin 13
int inPin = 7;   // pushbutton connected to digital pin 7
int val = 0;     // variable to store the read value

void setup()
{
  pinMode(ledPin, OUTPUT);      // sets the digital pin 13 as output
  pinMode(inPin, INPUT);      // sets the digital pin 7 as input
}

void loop()
{
  val = digitalRead(inPin);   // read the input pin
  digitalWrite(ledPin, val);    // sets the LED to the button's value
}

Sets pin 13 to the same value as the pin 7, which is an input.

Note

If the pin isn't connected to anything, digitalRead() can return either HIGH or LOW (and this can change randomly).
The analog input pins can be used as digital pins, referred to as A0, A1, etc.

digitalWrite()

Description

Write a HIGH or a LOW value to a digital pin.
If the pin has been configured as an OUTPUT with pinMode(), its voltage will be set to the corresponding value: 5V (or 3.3V on 3.3V boards) for HIGH, 0V (ground) for LOW.
If the pin is configured as an INPUT, writing a HIGH value with digitalWrite() will enable an internal 20K pullup resistor. Writing LOW will disable the pullup. The pullup resistor is enough to light an LED dimly, so if LEDs appear to work, but very dimly, this is a likely cause. The remedy is to set the pin to an output with the pinMode() function.
NOTE: Digital pin 13 is harder to use as a digital input than the other digital pins because it has an LED and resistor attached to it that's soldered to the board on most boards. If you enable its internal 20k pull-up resistor, it will hang at around 1.7 V instead of the expected 5V because the onboard LED and series resistor pull the voltage level down, meaning it always returns LOW. If you must use pin 13 as a digital input, use an external pull down resistor.

Syntax

digitalWrite(pin, value)

Parameters

pin: the pin number
value: HIGH or LOW

Returns

none

Example

 
int ledPin = 13;                 // LED connected to digital pin 13

void setup()
{
  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
}

void loop()
{
  digitalWrite(ledPin, HIGH);   // sets the LED on
  delay(1000);                  // waits for a second
  digitalWrite(ledPin, LOW);    // sets the LED off
  delay(1000);                  // waits for a second
}

Sets pin 13 to HIGH, makes a one-second-long delay, and sets the pin back to LOW.

Note

The analog input pins can be used as digital pins, referred to as A0, A1, etc.

pinMode()

Description

Configures the specified pin to behave either as an input or an output. See the description of digital pins for details on the functionality of the pins.
As of Arduino 1.0.1, it is possible to enable the internal pullup resistors with the mode INPUT_PULLUP. Additionally, the INPUT mode explicitly disables the internal pullups.

Syntax

pinMode(pin, mode)

Parameters

pin: the number of the pin whose mode you wish to set
mode: INPUT, OUTPUT, or INPUT_PULLUP.

Returns

None

Example

int ledPin = 13;                 // LED connected to digital pin 13

void setup()
{
  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
}

void loop()
{
  digitalWrite(ledPin, HIGH);   // sets the LED on
  delay(1000);                  // waits for a second
  digitalWrite(ledPin, LOW);    // sets the LED off
  delay(1000);                  // waits for a second
}

Note

The analog input pins can be used as digital pins, referred to as A0, A1, etc.

constants

Constants are predefined variables in the Arduino language. They are used to make the programs easier to read. We classify constants in groups.

Defining Logical Levels, true and false (Boolean Constants)

There are two constants used to represent truth and false in the Arduino language: true, and false.

false

false is the easier of the two to define. false is defined as 0 (zero).

true

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is true, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.
Note that the true and false constants are typed in lowercase unlike HIGH, LOW, INPUT, & OUTPUT.

Defining Pin Levels, HIGH and LOW

When reading or writing to a digital pin there are only two possible values a pin can take/be-set-to: HIGH and LOW.
HIGH
The meaning of HIGH (in reference to a pin) is somewhat different depending on whether a pin is set to an INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report HIGH if a voltage of 3 volts or more is present at the pin.
A pin may also be configured as an INPUT with pinMode, and subsequently made HIGH with digitalWrite, this will set the internal 20K pullup resistors, which will steer the input pin to a HIGH reading unless it is pulled LOW by external circuitry. This is how INPUT_PULLUP works as well
When a pin is configured to OUTPUT with pinMode, and set to HIGH with digitalWrite, the pin is at 5 volts. In this state it can source current, e.g. light an LED that is connected through a series resistor to ground, or to another pin configured as an output, and set to LOW.
LOW
The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW if a voltage of 2 volts or less is present at the pin.
When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, e.g. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH.

Defining Digital Pins, INPUT, INPUT_PULLUP, and OUTPUT

Digital pins can be used as INPUT, INPUT_PULLUP, or OUTPUT. Changing a pin with pinMode() changes the electrical behavior of the pin.

Pins Configured as INPUT

Arduino (Atmega) pins configured as INPUT with pinMode() are said to be in a high-impedance state. Pins configured as INPUT make extremely small demands on the circuit that they are sampling, equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.
If you have your pin configured as an INPUT, you will want the pin to have a reference to ground, often accomplished with a pull-down resistor (a resistor going to ground).

Pins Configured as INPUT_PULLUP

The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on.

Pins Configured as Outputs

Pins configured as OUTPUT with pinMode() are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can source (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for reading sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. The amount of current provided by an Atmega pin is also not enough to power most relays or motors, and some interface circuitry will be required.

if (conditional) and ==, !=, <, > (comparison operators)

if, which is used in conjunction with a comparison operator, tests whether a certain condition has been reached, such as an input being above a certain number. The format for an if test is:

if (someVariable > 50)
{
  // do something here
}

The program tests to see if someVariable is greater than 50. If it is, the program takes a particular action. Put another way, if the statement in parentheses is true, the statements inside the brackets are run. If not, the program skips over the code.
The brackets may be omitted after an if statement. If this is done, the next line (defined by the semicolon) becomes the only conditional statement.

if (x > 120) digitalWrite(LEDpin, HIGH); 

if (x > 120)
digitalWrite(LEDpin, HIGH); 

if (x > 120){ digitalWrite(LEDpin, HIGH); } 

if (x > 120){ 
  digitalWrite(LEDpin1, HIGH);
  digitalWrite(LEDpin2, HIGH); 
}                                 // all are correct

The statements being evaluated inside the parentheses require the use of one or more operators:

Comparison Operators:

 x == y (x is equal to y)
 x != y (x is not equal to y)
 x <  y (x is less than y)  
 x >  y (x is greater than y) 
 x <= y (x is less than or equal to y) 
 x >= y (x is greater than or equal to y)

Warning:

Beware of accidentally using the single equal sign (e.g. if (x = 10) ). The single equal sign is the assignment operator, and sets x to 10 (puts the value 10 into the variable x). Instead use the double equal sign (e.g. if (x == 10) ), which is the comparison operator. The latter statement is only true if x equals 10, but the former statement will always be true.

if / else

if/else allows greater control over the flow of code than the basic if statement, by allowing multiple tests to be grouped together. For example, an analog input could be tested and one action taken if the input was less than 500, and another action taken if the input was 500 or greater. The code would look like this:

if (pinFiveInput < 500)
{
  // action A
}
else
{
  // action B
}

else can proceed another if test, so that multiple, mutually exclusive tests can be run at the same time.
Each test will proceed to the next one until a true test is encountered. When a true test is found, its associated block of code is run, and the program then skips to the line following the entire if/else construction. If no test proves to be true, the default else block is executed, if one is present, and sets the default behavior.
Note that an else if block may be used with or without a terminating else block and vice versa. An unlimited number of such else if branches is allowed.

if (pinFiveInput < 500)
{
  // do Thing A
}
else if (pinFiveInput >= 1000)
{
  // do Thing B
}
else
{
  // do Thing C
}

Another way to express branching, mutually exclusive tests, is with the switch case statement.

for statements

Desciption

The for statement is used to repeat a block of statements enclosed in curly braces. An increment counter is usually used to increment and terminate the loop. The for statement is useful for any repetitive operation, and is often used in combination with arrays to operate on collections of data/pins.
There are three parts to the for loop header:
for (initialization; condition; increment) {
//statement(s);
}

The initialization happens first and exactly once. Each time through the loop, the condition is tested; if it's true, the statement block, and the increment is executed, then the condition is tested again. When the condition becomes false, the loop ends.

Example

// Dim an LED using a PWM pin
int PWMpin = 10; // LED in series with 470 ohm resistor on pin 10

void setup()
{
  // no setup needed
}

void loop()
{
   for (int i=0; i <= 255; i++){
      analogWrite(PWMpin, i);
      delay(10);
   } 
}

Coding Tips Using For Loop

These types of unusual for statements may provide solutions to some rare programming problems.
For example, using a multiplication in the increment line will generate a logarithmic progression:

for(int x = 2; x < 100; x = x * 1.5){
println(x);
}

Generates: 2,3,4,6,9,13,19,28,42,63,94
Another example, fade an LED up and down with one for loop:

void loop()
{
   int x = 1;
   for (int i = 0; i > -1; i = i + x){
      analogWrite(PWMpin, i);
      if (i == 255) x = -1;             // switch direction at peak
      delay(10);
   } 
}

switch / case statements

Like if statements, switch...case controls the flow of programs by allowing programmers to specify different code that should be executed in various conditions. In particular, a switch statement compares the value of a variable to the values specified in case statements. When a case statement is found whose value matches that of the variable, the code in that case statement is run.
The break keyword exits the switch statement, and is typically used at the end of each case. Without a break statement, the switch statement will continue executing the following expressions ("falling-through") until a break, or the end of the switch statement is reached.

Example

  switch (var) {
    case 1:
      //do something when var equals 1
      break;
    case 2:
      //do something when var equals 2
      break;
    default: 
      // if nothing else matches, do the default
      // default is optional
  }

Syntax

switch (var) {
  case label:
    // statements
    break;
  case label:
    // statements
    break;
  default: 
    // statements
}

Parameters

var: the variable whose value to compare to the various cases
label: a value to compare the variable to

while loops

Description

while loops will loop continuously, and infinitely, until the expression inside the parenthesis, () becomes false. Something must change the tested variable, or the while loop will never exit. This could be in your code, such as an incremented variable, or an external condition, such as testing a sensor.

Syntax

while(expression){
  // statement(s)
}

Parameters

expression - a (boolean) C statement that evaluates to true or false

Example

var = 0;
while(var < 200){
  // do something repetitive 200 times
  var++;
}

do - while

The do loop works in the same manner as the while loop, with the exception that the condition is tested at the end of the loop, so the do loop will always run at least once.

do
{
    // statement block
} while (test condition);

Example

do
{
  delay(50);          // wait for sensors to stabilize
  x = readSensors();  // check the sensors

} while (x < 100);

break

break is used to exit from a do, for, or while loop, bypassing the normal loop condition. It is also used to exit from a switch statement.

Example

for (x = 0; x < 255; x ++)
{
    digitalWrite(PWMpin, x);
    sens = analogRead(sensorPin);  
    if (sens > threshold){      // bail out on sensor detect
       x = 0;
       break;
    }  
    delay(50);
} 

continue

The continue statement skips the rest of the current iteration of a loop (do, for, or while). It continues by checking the conditional expression of the loop, and proceeding with any subsequent iterations.

Example

for (x = 0; x < 255; x ++)
{
    if (x > 40 && x < 120){      // create jump in values
        continue;
    }

    digitalWrite(PWMpin, x);
    delay(50);
}

return

Terminate a function and return a value from a function to the calling function, if desired.

Syntax:

return;
return value; // both forms are valid

Parameters

value: any variable or constant type

Examples:

A function to compare a sensor input to a threshold

int checkSensor(){       
    if (analogRead(0) > 400) {
        return 1;
    else{
        return 0;
    }
}

goto

Transfers program flow to a labeled point in the program

Syntax

label:
goto label; // sends program flow to the label

Tip

The use of goto is discouraged in C programming, and some authors of C programming books claim that the goto statement is never necessary, but used judiciously, it can simplify certain programs. The reason that many programmers frown upon the use of goto is that with the unrestrained use of goto statements, it is easy to create a program with undefined program flow, which can never be debugged.
With that said, there are instances where a goto statement can come in handy, and simplify coding. One of these situations is to break out of deeply nested for loops, or if logic blocks, on a certain condition.

Example

for(byte r = 0; r < 255; r++){
    for(byte g = 255; g > -1; g--){
        for(byte b = 0; b < 255; b++){
            if (analogRead(0) > 250){ goto bailout;}
            // more statements ... 
        }
    }
}
bailout:

In an Arduino Program/Sketch you will see two main functions, setup() & other is loop ().

We firstly describe setup() function....

setup()

The setup() function is called when a sketch/program of Arduino starts. We use it to initialize variables, pin modes(Input/Output), start using libraries, etc. The setup function will only run once, after each powerup or reset of the Arduino board.

Example

 
int buttonPin = 3;

void setup()
{
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

void loop()
{
  // ...
} 

loop()

After creating a setup() function, which initializes and sets the initial values, the loop() function does precisely what its name suggests, and loops consecutively, allowing your program to change and respond. We use it to actively control the Arduino board.

Example

 
const int buttonPin = 3;

// setup initializes serial and the button pin
void setup()
{
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}



void loop()// loop checks the button pin each time,
{
  if (digitalRead(buttonPin) == HIGH)// and will send serial if it is pressed
    Serial.write('H');
  else
    Serial.write('L');

  delay(1000);
} 

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