threadfor, threadendfor

Purpose

Begins a parallel for loop.

Format

threadfor i (start, stop, step);
  .
  .
  .
threadendfor;

Parameters

i:(literal) the name of the counter variable.
start:(scalar) the initial value of the counter.
stop:(scalar) the final value of the counter.
step:(scalar) the increment value.

Examples

Example 1

// A basic 'threadfor' loop
threadfor i (1, 4, 1);
    print i;
threadendfor;

The code above, will print out:

1.000
2.000
3.000
4.000

Simple bootstrap of the mean of one variable

// Create fully pathed name of dataset
dataset = getGAUSSHome() $+ "examples/fueleconomy.dat";

// Load all contents of dataset
x = loadd(dataset);

// Extract 2nd column
engine_disp = x[., 2];

iters = 500;
nobs = rows(engine_disp);

// Pre-allocate vector to hold sample means
sample_means = zeros(iters, 1);

threadFor i(1, iters, 1);
    // Create tmp variable 'idx',
    // containing random integers from 1-nobs
    //'idx' exists ONLY during the loop
    idx = ceil(nobs * rndu(nobs, 1));

    // Extract random sample into tmp variable,
    //'sample'. Only exists during loop
    sample = engine_disp[idx];

    // Calculate mean of sample
    // and assign using loop counter
    //'sample_means' will persist after loop
    sample_means[i] = meanc(sample);
threadEndFor;

Remarks

  1. The iterations of a threadfor, threadendfor loop may execute in any order.

  2. Indexed assignments to global variables that use the loop counter behave the same as in a standard for loop.

  3. Non-indexed assignments will create a temporary variable that persists only through the remainder of the current loop iteration. For example:

    a = 34.7;
    threadfor i(1, 2, 1);
        a = rndu(1,1);
        print a;
    threadEndfor;
    
    print a;
    

    will produce output similar to the following:

    0.90560157
    0.52594285
    34.700000
    
  4. threadfor, threadendfor loops may not be nested

  5. Debugging inside of threadfor, threadendfor loops is currently not supported.

See also

Performance considerations