Matlab is unable to evaluate very a very long expression

Question

Dominik Hiltbrunner 2021-11-5

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1579664-matlab-is-unable-to-evaluate-very-a-very-long-expression

编辑： Dominik Hiltbrunner 2021-11-5

采纳的回答： Steven Lord

very_long_expression.txt

在 MATLAB Online 中打开

Attached to this post is a text file containing a very long expression.

I want to evaluate this expression numerically in a Matlab function, i.e. something like this:

function result = (<long lost of all the parameters>)
    result = '<this very long expression from the text file>'
end

The computer gets stuck when doing so, not returning a result even after hours of running.

Is there anything I can do to speed up the computation of very long expressions?

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Stephen23 2021-11-5

Note that you should replace all of the ^(1/2) with SQRT.

What sizes are the input arrays?

Are you intentionally using matrix operations instead of array operations everywhere in this code?

Dominik Hiltbrunner 2021-11-5

The ^(1/2) terms are in fact generated by Matlab itself, i.e. the long expression also comes from a Matlab file in which my sqrt(...) inputs are then printed in this way. Can I prevent Matlab from doing so?

Every variable in this expression is a scalar, no arrays or matrix operations are performed.

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Answer 1

Steven Lord 2021-11-5

1
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https://ww2.mathworks.cn/matlabcentral/answers/1579664-matlab-is-unable-to-evaluate-very-a-very-long-expression#answer_824614

How did you generate this long expression? Did you generate this using Symbolic Math Toolbox? If so consider using matlabFunction to create a function file from this expression (leaving the 'Optimize' option set to its default value of true) and see if the optimization process simplifies the computation of that expression by extracting out some common terms that it can compute once and use repeatedly.