EVAL do not display OUTPUT

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Miroslav Mitev 2018-9-5

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评论： Steven Lord 2020-11-2

Hi all,

I am using eval function but even if I put semicolon ";" at the end of the line Matlab shows the output in the command window.

Is it possible to not display the result in the command window?

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Answer 1

OCDER 2018-9-5

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编辑：OCDER 2018-9-5

在 MATLAB Online 中打开

"I am using eval function but"

Don't use eval. It's one of those functions that's there but not to be used unless absolutely necessary, which is almost never. eval creates very inefficient, hard-to-debug codes.

https://blogs.mathworks.com/loren/2005/12/28/evading-eval/

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

For your case, use fprintf or disp to display variables you want. Otherwise, use the ";" to silence the output.

A = rand(3)   %creates and shows A
A = rand(3);  %silenced output for A
disp(A);      %shows A

I am guessing you did something like this:

eval('A = rand(3)');  %Does not silence output for A = rand(3)
eval('A = rand(3);')  %Silences output A = rand(3). But why bother using eval???

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WinCento99 2020-11-2

编辑：WinCento99 2020-11-2

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hey OCDER, can you suggest how to replace eval or something else?

%% Initial structuring
y = [1 2] ;
f = @(y) [y bsxfun(@minus,sin(y(end)),y(end-1))] ;
%% Direct loop
for i = 1:19
y = f(y) ;
end
%% Loop with anonymous function --
%  How can I have y after the loop with the true output?
fun = @(x) eval(['for i = 1:' num2str(x) '; y = f(y); end;']);
fun(19)

How can I have y after the loop with the true output?

Steven Lord 2020-11-2

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What you've written will not work for a couple different reasons, the first of which is that it attempts to create the variable i in the anonymous function's workspace.

Not every piece of code is suitable for conversion into an anonymous function. I would define your fun as a regular old function.

function y = fun(f, y, x)
for iter = 1:x
    y = f(y);
end
end

If you nested this inside the function where you wanted to call it, you could share f and y with that workspace and avoid having to pass them into fun.

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