Unspecified behaviour of function imag.

In version '9.10.0.1602886 (R2021a)', running

imag part

ans = 1×4

0 0 0 0

will return

[0 0 0 0]

ans = 1×4

0 0 0 0

I accidentally found this when trying to type "imagpart". How does this happen? Will it affect our program in other unanticipated ways?

Answer 1

[Walter Roberson]

This will not affect your code.

You are encountering Command/Function Duality https://www.mathworks.com/help/matlab/matlab_prog/command-vs-function-syntax.html

When you call

imag part

that is the same as if you had invoked

imag('part')

which is calling imag() on the vector of four characters, 'p', 'a', 'r', 't' .

In many circumstances, characters automatically convert to the numeric codes used to internally encode the characters, such as 112 for 'p', and 97 for 'a' . So imag() treats this as a vector of real-valued double precision numbers. But the imaginary() portion of those is all 0 so 0 0 0 0 gets returned.