# What are the differences between laplace & fourier trans

1. ## difference between laplace and fourier transform

What are the differences?
I mean when we will make a decision "hmm now i must use laplace transform or now i must use fourier transform".

What are the absences in laplace transform so fourier design a new transfom?

I want to know these transforms' main idea, differences.

Thanks .
Sincerely;

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2. ## laplace vs fourier

for all signals we can have laplace transform but we can have fourier transform only for ceratin cases...Fourier transform needs certain conditions caled as Dirchlet conditions whereas laplace wont need anything like this....

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3. ## difference between laplace and fourier

Originally Posted by electronics_kumar
for all signals we can have laplace transform but we can have fourier transform only for ceratin cases...Fourier transform needs certain conditions caled as Dirchlet conditions whereas laplace wont need anything like this....
Can you explain this concept please?I need some details..

Thanks...

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4. ## fourier vs laplace

Originally Posted by serimc
Originally Posted by electronics_kumar
for all signals we can have laplace transform but we can have fourier transform only for ceratin cases...Fourier transform needs certain conditions caled as Dirchlet conditions whereas laplace wont need anything like this....
Can you explain this concept please?I need some details..

Thanks...
http://lofi.forum.physorg.com/Laplac...urier_403.html

http://www.dsprelated.com/showmessage/39243/1.php

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5. ## laplace vs. fourier

in a simple expression:

Laplas Transform does a real transformation on complex data but Fourier Tranform does a complex transformation on real data.
it means:

L(σ1+jω1)=σ2+jω2
F(ω1)=|ω2|<ω2

at the presence of some condition you can take the Fourier transformation by placing instead of s in Laplas tranform.

6. ## laplace vs fourier transform

theoretically..laplace represents σ + jw and is in all of the s-plane while in fourier its only in the jw axis of this s-plane..so basically we are setting the real part of the exponenntial to 0 and hence
it will give you the features for steady state for a sinusoidal input
and in the case of laplace it will tel u for rising or fallin sinusoidal.
i hope that shud answer ur question..

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7. ## laplas transform

For a good explanation you can consult the book PLL, or Roland E. Best, that you can find in this forum.

As my colegees said Laplace transform translate f(t) to σ + ωi domain, while Fourier translate f(t) to w domain.

that means Laplace has information of time and frequency that's why we use to study transitory circuits. But Fourier dosn't have all the information i this case fase and wave forms only frecquency and amplitude.

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8. ## fourier versus laplace

Originally Posted by shivamrules
theoretically..laplace represents σ + jw and is in all of the s-plane while in fourier its only in the jw axis of this s-plane..so basically we are setting the real part of the exponenntial to 0 and hence
it will give you the features for steady state for a sinusoidal input
and in the case of laplace it will tel u for rising or fallin sinusoidal.
i hope that shud answer ur question..

for lapalce transform, it is (σ + jw) when you are going to Fourier transform it become (0 + jw )..i mean σ =0 no attenuation in the system...

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