Matlab Tools for Multiple Instruction Single Data (MISD)?

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Juan Pablo Segovia 2017-5-8

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评论： Walter Roberson 2017-5-9

Hello, I have a problem that has more than one million functions to evaluate, all different, for the same data group. Morphologically this type of problem is called MISD (Multiple Instructions Single Data), each mathematical function can be written as a matlab function, with input and output arguments. What is the most efficient way to solve this type of problems with matlab ?.

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Jan 2017-5-8

It depends on how the functions are stored. Please give us a small example.

Juan Pablo Segovia 2017-5-8

编辑：Walter Roberson 2017-5-8

在 MATLAB Online 中打开

Jan,

Thanks for your interest in the problem, for example: the main program declares the global variables,

Name Size        Bytes  Class Attributes
N1  1x1             8  double global
N6  1x1             8  double global
Px 82251x1     658008  double global
S 4496388x6 215826624  double global
V = test0001;

For higher execution speed all the functions were explicitly generated:

% Funtion test0001
Function vpe = test0001
Global s px n1 n6
Vpe = - ((s (px, 2) -n6 + 1). * (S (px, 2) -n6 + 2) * (s (px, 2) -n6 + 3)) / 6;
Return

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Answer 1

Walter Roberson 2017-5-8

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global variables are the slowest kind of variables. You would be better to parameterize your functions

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Walter Roberson 2017-5-8

Are the functions written in their own .m files, or are they anonymous functions, perhaps even created dynamically?

Are the same functions used over and over? If it is, then it might be practical to do some kind of transformation into another programming language that might be more efficient to execute.

Your sample function uses s(px,2) multiple times, which appears to be taking a subset of s. Would all of the functions be taking the same subset, or would px be varying over the different functions? Because if it is the same subset you could gain a lot of efficiency by extracting the subset before proceeding.

Is there a general pattern that the computations follow? If there is then that might make it easier to transform for higher efficiency.

I am thinking, for example, that maybe you could mechanically generate .cu files for GPU use; there would be overhead associated with that, but in some situations the overhead would be worth it.

By the way: none of the parallel processing facilities copy global variables.

Is it correct that what you show as global variables are essentially constants to the batch of computations?

Juan Pablo Segovia 2017-5-9

Walter, many thanks to you for the advice, you have some examples of similar code or you can recommend me bibliography related to this subject.

I reiterate my gratitude, sincerely J.P.

Walter Roberson 2017-5-9

If you have a vector of symbolic expressions, I would probably be tempted to factor() the length of the vector, reshape() with the last (largest) factor as the first dimension, then use matlabFunction on each column, asking to generate files. The purpose here is to batch enough work together to make it worth while to talk to a worker considering communications overhead.

If the expressions are to be reused multiple times, leave the default matlabFunction optimization on; otherwise, the optimization phase might be more expense than it is worth.

After that you can create workers, AddAttachedFiles, and parfeval() to invoke the functions on the current data.

Note: matlabFunction does not currently do well on vectors of functions where the components might require looping or piecewise(): in current implementations it tries put 'if' statements inside the horzcat or vertcat operator. matlabFunction also currently does not do well on int() with a vector of locations to be integrated.

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Matlab Tools for Multiple Instruction Single Data (MISD)?

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