Passing no of colours in colormap as a variable

Question

Naveen 2013-2-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/64092-passing-no-of-colours-in-colormap-as-a-variable

Hi,

I am plotting several different contour plots in a code. The code for plotting them is below. My problem is that for publication purpose, I want to use 3500 colours instead of 500 (as shown below) since the figure then looks smooth. But obviously Matlab runs extremely slow on my Mac. I wanted to pass no. of colours as a variable and change it at one place. So that I don't need to change it at several places in the code. When I pass the variable e.g. noColors = 3500, Matlab complains at colormap jet() line saying it needs finite values. How to play around this problem?

 contourf( a0Grid, omegaPGrid, log10(freqShift), 500, 'Edgecolor', 'none' )
 colormap jet(500)

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Image Analyst 2013-2-19

But colormap(jet(noColors)) does? I didn't know that there would be a difference between the function call method and the command line method of calling colormap. It would be interesting to know the reason for that. I know there is a difference for some functions, like those that take a filename such as load() or save().

Walter Roberson 2013-2-19

在 MATLAB Online 中打开

colormap jet(500)

is equivalent to

colormap('jet(500)')

which is not a documented facility. It happens to work because colormap() feval()'s its argument when its argument is a string, but the documentation doesn't say that. The one example uses the function form equivalent to

colormap(jet(500))

which calls jet(500) and returns that numeric array as the argument to colormap()

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Answer 1

Walter Roberson 2013-2-19

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/64092-passing-no-of-colours-in-colormap-as-a-variable#answer_75705

在 MATLAB Online 中打开

Try

colormap(jet(noColors))

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Walter Roberson 2013-2-20

在 MATLAB Online 中打开

When you have

A B(C)

then due to MATLAB's "command / function equivalence", what would be passed to the function "A" would be the string 'B(C)'. "A" would then be responsible for interpreting the string. It happens that colormap() processes received strings using feval() or eval() and so runs whatever code is there, but that is more of an exception.

For example,

cd hotpink(128)

is not going to call hotpink(128): instead it would try to cd to a directory literally named 'hotpink(128)' complete with the () in the name.

When you use

A(B(C))

instead, then B(C) is evaluated as an expression, and the result (whatever data type it happens to be) is passed into A.

Naveen 2013-2-20