MATLAB: Does Isreal function give wrong answer after using collect function

basic function

In the code below, the second function isreal gives wrong answer after using collect function.

clear all;
close all;
clc;
syms w real;
m=w^3-1i*w^2+2*w-1i;
mre=real(m)
isreal(mre)
mrecol=collect(real(m),w)
isreal(mrecol)

Best Answer

There is no isreal() function for sym specifically, so the result of both isreal() calls is undefined. But double check class(mre) and class(mrecol)

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MATLAB: Plotting a complex function with function in real and imag part

figure,plot(w,real(f)) hold on,plot(w,imag(f))

figure,plot(w,[real(x);imag(x)])

MATLAB: Does NaN==NaN give zero while isnumeric(NaN) and isreal(NaN) give 1

This is not a contradiction or a bug in MATLAB, rather this is the way NaN is defined. The function call ISREAL(NaN) returns 1 (true) because NaN has no imaginary part.

ISNUMERIC(NaN) is true as NaN is stored in a double array (i.e. is it not a char array, structure, cell array, etc.)

When you compare a NaN value with NaN, you are comparing two numbers which have no defined values. Thus, the comparison returns 0 (false).

The best logical test that can be performed on NaN uses the builtin ISNAN function. We strongly recommended that you use the ISNAN function to find NaN entries of a double array. This is illustrated in the following example:

b=NaN;
test=(b==NaN)
testisnan=isnan(b)

The above code results in

 test =
      0
 testisnan =
      1

Best Answer

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MATLAB: Plotting a complex function with function in real and imag part

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