Why this message appears?

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taher zaouali 2019-5-1

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评论： Star Strider 2019-5-4

clear all;
f1=200;
f2=250;
a1=1;
a2=1.5;
fe=10e3;
temps=0:1/fe:0.02-1/fe;
m1=a1*sin(2*pi*f1*temps);
m2=a2*sin(2*pi*f2*temps);
mt=m1*m2;

Error using *

Inner matrix dimensions must agree.

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Star Strider 2019-5-1

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It appears because you are multiplying two row vector using matrix mulktiplication.

You need to use element-wise array multiplication (using .* instead of *):

mt = m1 .* m2;

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taher zaouali 2019-5-4

I've figured it out:

spec_mt=fft(mt,n);
plot(freqs,abs(spec_mt));grid;

the comma is between 2 parts of the fft not of the abs.

Thanks for the help.

Star Strider 2019-5-4

As always, my pleasure.

I took the ‘n’ out of the fft call entirely. I was not certain where you wanted to put the ‘n’, or what you wanted to do with it. If ‘n’ is the same as the size as the time-domain vector, using it as the size of the fft does not change anything, because the length of the time-domain vector is the default length of the fft for that vector.

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