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

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Shreya
Shreya 2023-3-24
编辑： Dyuman Joshi 2023-3-24
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?

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回答（2 个）

Walter Roberson
Walter Roberson 2023-3-24
编辑：Walter Roberson 2023-3-24
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
Dyuman Joshi
Dyuman Joshi 2023-3-24
编辑：Dyuman Joshi 2023-3-24
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

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