Diffusion Equation Homework: Show Formula (8) Makes Sense for 0 < t < 1/(4ak)

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SUMMARY

The discussion centers on the diffusion equation solution represented by formula (8), specifically u(x,t)=1/√(4*pi*k*t) ∫ e-(x-y)²/4ktP(y) dy. It is established that this formula is valid for the time interval 0 < t < 1/(4ak), as the convergence of the integral relies on the behavior of the function P(x) and the exponential decay governed by the term e-(x-y)²/4kt. The participants clarify that for larger values of t, the integral may not converge, thus rendering the solution invalid.

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Homework Statement


Hello, I don't understand the solution of an exercise

Let P(x) be a continuous function such that |P(x)|≤Ceax² .
Show that formula (8) for the solution of the diffusion equation makes sense for 0 < t < 1/(4ak), but not necessarily for larger t.

Homework Equations


Equation (8) refers to
u(x,t)=1/√(4*pi*k*t) ∫ e-(x-y)²/4ktP(y) dy

The Attempt at a Solution


The solution just says that
upload_2016-2-24_20-21-14.png


I don't understand how they conclude ? I don't see why we have 0 < t < 1/(4ak)

Thanks
 
Physics news on Phys.org
Consider the sign of the ##y^2## term in the exponent. What has to be true for the integral to converge?
 
vela said:
Consider the sign of the ##y^2## term in the exponent. What has to be true for the integral to converge?
I see, thanks !
 

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