Error message when using plot command: "Subscript indices must either be real positive integers or logicals"

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Kelsey 2013-10-10

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评论： dpb 2013-10-10

I am having an issue when I run this code:

x = linspace(0,1,7);
yprimeexact = -2*x.*exp(-x.^2);
yprimeapprox = [-1.3264656E-02 -0.3154821 -0.5814109 -0.7609767 -0.8383472 -0.8199028 -0.7577648];
plot(x,yprimeexact,'b')
hold on
plot(x,yprimeapprox,'r')

When I try to plot the data, I get an error message saying, "Subscript indices must either be real positive integers or logicals." Do you know what is wrong? Thank you in advance!

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dpb 2013-10-10

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Looks like you've inadvertently created an array named plot earlier...

clear plot

then try again. If that doesn't cure it, do

which plot

and post it and the full error in context but I suspect it will...

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Answer 1

Wayne King 2013-10-10

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The above code should execute properly Kelsey. Perhaps you have a variable named linspace() in your workspace?

If you execute

>>who linspace

do you get something back, like "Your variables are"

If so try

>> clearvars linspace

and try again. Worse case, just clear everything and copy and paste the above code back into the workspace, it should work.

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Sean de Wolski 2013-10-10

Could also be a shadowed plot.m function which inside does indexes into x or similar.

dpb 2013-10-10

which was my first suggestion of likely cause but seems if OP really did what says did (and didn't do the wrong thing again right after which we can't see) should've gone away.

But, then again, if is running a script that has the problematic line in it and we're not seeing that, then it's quite possible that the problem gets fixed at the command line then runs the script that has the error and makes the problem all over again-- ad nauseum, so to speak... :)

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Answer 2

Sean de Wolski 2013-10-10

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Run:

dbstop if error

At the command line.

Then run the above code. It will stop with the debugger on the offending line and you will be able to see which function (e.g. exp, plot, linspace has a variable named after it or another function shadowing the builtin one.