Getting an error "Error using erfc... Input must be real and full"

This code is giving the error msg "Error using erfc... Input must be real and full"

Here PR = 0.71 so "a" will be neagtive.

a=M/(PR-1)

exp(-y*sqrt(a*PR)).*erfc(eta*sqrt(PR)-sqrt(a*t))+exp(y*sqrt(a*PR)).*erfc(eta*sqrt(PR)+sqrt(a*t))

How to rectify this problem?

Answer 1

[Walter Roberson]

if a is negative and t is positive then sqrt(a*t) is square root of a negative value which is imaginary. You end up taking erfc of a complex value.

If you really need erfc of a complex value see https://www.mathworks.com/matlabcentral/answers/7153-erfc-with-complex-number#answer_9795

Answer 2

[Dyuman Joshi]

The function erfc only supports real inputs (as evident by the error) and the input to erfc here is complex.

You can either use the symbolic erfc function, which requires Symbolic Math Toolbox. Note that you need to pass the input as symbolic number or symbolic variable.

Or you can use FEX file submissions -

erfi function

Error function for complex numbers