find minimum value of a two-variable equation on an interval.

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miaomiao tang 2020-2-25

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https://ww2.mathworks.cn/matlabcentral/answers/507446-find-minimum-value-of-a-two-variable-equation-on-an-interval

回答： dpb 2020-2-25

Hi,

I searched a lot about this question but I still have a trouble in deleting the . when I run the code,

[x y] = meshgrid(1:0.01:2*pi,1:0.01:2*pi);
y     = 4*x.^2 + 5*y.^2;
min(min(y));

I dont want copy the equation y every time when I am doing an experiment that have a lot of data.

Thanks!

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dpb 2020-2-25

Not sure what the real question is...couple comments:

You overwrite y when computing the functional; if want to keep it, write z=... instead.
The idiom min(min()) can be written as either zmin=min(z(:)): or if have release R2018b or later as zmin=min(z,'all');

If those don't match what looking for, explain further...

miaomiao tang 2020-2-25

Thanks for your answer, and sorry for the misunderstanding.

My experiment process will generate a two-variable equation so I have to copy and paste the eqaution every time and put the dot in.

There is a dot between every element like .^, so is there anyway I can delet the dot but the equation can still work?

Thanks!

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Answer 1

dpb 2020-2-25

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"...is there anyway I can delet[e] the dot but the equation can still work?"

Ah! Indeed I didn't follow along the nub of the question.

Yes, but not with vectorized inputs; you'd then have to either write the loop explicitly or use arrayfun to process the inputs.

The "dot" operators are mandatory to evaluate the elements of the input arrays as element-by-element operations; otherwise they will be matrix operators which is not what is wanted/needed here.

However, MATLAB is thinking about that for you, already! :) Don't try to swim upstream, instead of trying to evaluate the non-vectorized version, vectorize it instead.

Need more information on the manner in which this "experiment process" is implemented; I'd guess there may be a way to automate the transfer to (say) a text file which could be read into a string which could subsequently be modified as needed by inserting the dot operators via vectorize. The string could then be converted to the functional with str2func