How to plot different functions of different colors in the same figure in a FOR cycle

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Francesco 2014-8-30

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评论： Stephen23 2014-9-2

I have to plot different functions in the same figure with a FOR cycle, each with a different color by others. I've tried to build a character array but when I plot, the error is "Error using plot. Conversion to double from function_handle is not possible.". How can I solve it? Thanks

Parts of the code are:

char = {'k--' 'ro-' 'bs-' 'g^-'};

(...)

ichar = char(jj)

(...)

plot(xex, uex(xex), ichar);

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Stephen23 2014-9-2

Although the answers below mention this, it deserves to be stated clearly right here next to the question:

Do NOT define variables (or functions) with the same names as inbuilt functions, e.g. char in this example. It will cause all sorts of problems that you really just don't want to get into...

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Answer 1

dpb 2014-8-30

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编辑：dpb 2014-8-30

在 MATLAB Online 中打开

Almost there...

ch = {'k--' 'ro-' 'bs-' 'g^-'}; 
for i=1:4
  plot(rand(10,1),ch{i})
 if i==1, hold on, end
end

NB: the {} "curlies" to dereference the cell array instead of just the brackets.

BTW, note that didn't use "char" as a variable; char is a Matlab builtin function to build a character string array.

ADDENDUM

The pertinent section of code regarding a function handle isn't shown -- perhaps you've inadvertently aliased plot as well or the X,Y argument definitions aren't shown so the issue could be there as well...

Anyways, other than the previous aliasing of char noted, the error is in what isn't shown, not what is.

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dpb 2014-8-31

So what was the handle error?

Francesco 2014-9-2

The correction is:

ichar = char{jj};

with the {} brackets and non the () ones.

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Answer 2

Image Analyst 2014-8-30

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ColorOrder_demo.m

You might find it interesting how to set the default color order - the order that gets plotted when you don't specify a color at all. See the attached demo.

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Answer 3

Star Strider 2014-8-30

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在 MATLAB Online 中打开

The error you quoted is not in the code you quoted.

What are xex and uex?

Your line:

ichar = char(jj)

would return in ‘ichar’ whatever the ASCII chararacter corresponding to ‘jj’ was. It would probably correspond to a control character, with unpredictable results.

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dpb 2014-8-30

在 MATLAB Online 中打开

ichar = char(jj)

... would return in ‘ichar’ whatever the ASCII character corresponding to ‘jj'

Excepting he aliased the builtin char to a cell string array just ahead so that isn't the problem.

Image Analyst 2014-8-30

Don't you love it when they say "part of the code is..." and then don't give the part of the code that really makes a difference? For example we don't know if uex is an array or a scalar index, if "hold on" was called, if plot() is inside a loop, etc. And it makes a difference as to how we'd answer.

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