How to rewrite my expression using two abbreviations?

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Valeri Aronov 2021-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/868073-how-to-rewrite-my-expression-using-two-abbreviations

评论： Valeri Aronov 2021-7-4

I tried Rewrite Expression Using Abbreviations example in https://au.mathworks.com/help/symbolic/subexpr.html for subexpr() and I can't reproduce it - the code renders a new expression with sigma, but w/o sigma1 and sigma2.

This is a link to the answer to my another question that uses two abbreviations (sigma1 and sigma2):

https://au.mathworks.com/matlabcentral/answers/848785-how-to-get-rid-of-sign-in-diff-results#answer_718310

How do I get this result in MATLAB?

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Asmit Singh 2021-6-29

The question is not clear, can you tell what do you mean by sigma1 and sigma2

Valeri Aronov 2021-6-29

Both refs above have greek sigmas rendered as in https://en.m.wikipedia.org/wiki/Greek_letters_used_in_mathematics,_science,_and_engineering

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Walter Roberson 2021-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/868073-how-to-rewrite-my-expression-using-two-abbreviations#answer_736143

You get the pretty output only with Live Script

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Walter Roberson 2021-6-30

I mean that function displayVariable near line 81 of toolbox/symbolic/symbolic/@sym/display.m tests whether Live Script is being used, and if so then it invokes createMathML to create a MathML representation of the expression, and then calls matlab.internal.language.signalVariableDisplay to render the MathML .

The createMathML function runs code to detect useful sub-expressions and substitute generated variable names in place of sub-expressions, and adds nicely-formatted display of the generated variables after the main display.

The code to detect the sub-expressions and display them is not invoked if you are not using Live Script.

If you are not using Live Script, then you can use pretty(), which also does sub-expression detection and output, using a different form, using # followed by a number to indicate a replacement instead of using a named variable such as

. pretty() is useful sometimes, but the output can be kind of ugly.

So, to emphasize, that subexpr() example that you are looking at: they ran that example using Live Script, and the output with the

was generated by the functions that are called for Live Script. The

is not explicitly generated by the code you are executing in that example, which is why you have not been able to replicate the output.

Walter Roberson 2021-6-30

That was mostly for consistency. The important part is that I used semi-colon. It could have been coded [r;sigma] but not [r,sigma] because r is a column vector with more than one entry and adding a column with only one entry to that does not work.

Valeri Aronov 2021-7-4

A loosely-typed language like that may become challenging for a casual user like myself. I would say that the prompt help available from MATLAB gurus is a crucial piece of MATLAB usefulness. Thanks a lot.

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