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imag

Imaginary part of complex number

Syntax

imag(z)

Description

example

imag(z) returns the imaginary part of z. If z is a matrix, imag acts elementwise on z.

Examples

Compute Imaginary Part of Numeric Inputs

Find the imaginary parts of these numbers. Because these numbers are not symbolic objects, you get floating-point results.

[imag(2 + 3/2*i), imag(sin(5*i)), imag(2*exp(1 + i))]
ans =
    1.5000   74.2032    4.5747

Compute Imaginary Part of Symbolic Inputs

Compute the imaginary parts of the numbers converted to symbolic objects:

[imag(sym(2) + 3/2*i), imag(4/(sym(1) + 3*i)),  imag(sin(sym(5)*i))]
ans =
[ 3/2, -6/5, sinh(5)]

Compute the imaginary part of this symbolic expression:

imag(2*exp(1 + sym(i)))
ans =
2*exp(1)*sin(1)

Compute Imaginary Part of Symbolic Expressions

In general, imag cannot extract the entire imaginary parts from symbolic expressions containing variables. However, imag can rewrite and sometimes simplify the input expression:

syms a x y
imag(a + 2)
imag(x + y*i)
ans =
imag(a)
 
ans =
imag(x) + real(y)

If you assign numeric values to these variables or if you specify that these variables are real, imag can extract the imaginary part of the expression:

syms a
 a = 5 + 3*i;
imag(a + 2)
ans =
     3
syms x y real
imag(x + y*i)
ans =
y

Clear the assumption that x and y are real by recreating them using syms:

syms x y

Compute Imaginary Part for Matrix Input

Find the imaginary parts of the elements of matrix A:

syms x
A = [-1 + sym(i), sinh(x); exp(10 + sym(7)*i), exp(sym(pi)*i)];
imag(A)
ans =
[              1, imag(sinh(x))]
[ exp(10)*sin(7),             0]

Input Arguments

collapse all

Input, specified as a number, vector, matrix, or array, or a symbolic number, variable, array, function, or expression.

Tips

  • Calling imag for a number that is not a symbolic object invokes the MATLAB® imag function.

Alternatives

You can compute the imaginary part of z via the conjugate: imag(z)= (z - conj(z))/2i.

See Also

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Introduced before R2006a