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to find fourier transform of e^-t u(t). How do i remove this error

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Abhinav Raghunandan
Abhinav Raghunandan on 24 Mar 2021
Answered: Star Strider on 24 Mar 2021
syms t
>> y=ftransform(exp(-t),-20,20)
Unrecognized function or variable 'ftransform'.
>> y=fft(exp(-t),-20,20)
Error using fft
Invalid data type. First argument must be double, single, int8, uint8, int16, uint16, int32, uint32, or logical.

Answers (1)

Star Strider
Star Strider on 24 Mar 2021
The fourier function does not allow limits, so that integration would need to be done manually:
syms t omega
y = int(exp(-t).*exp(1j*omega*t), t, -20, 20)
y = simplify(y, 150)
y = rewrite(y, 'sincos')
y =
(2*sin(20*omega + 20i)*(omega - 1i))/(omega^2 + 1)
In LaTeX:

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