# Cumulative distribution function

• Apr 16th 2011, 10:56 AM
Nforce
Cumulative distribution function
We have cumulative distribution function Fx.

Fx = 1/1000x - 1/4

How do we get probability density function (gx) from Fx?

If we have gx, to get Fx, we need to integrate from 0 to x. Am I right?

So to get gx from Fx, we need to find the derivative, because it's an opposite operation from integration.
• Apr 16th 2011, 02:49 PM
mr fantastic
Quote:

Originally Posted by Nforce
We have cumulative distribution function Fx.

Fx = 1/1000x - 1/4

How do we get probability density function (gx) from Fx?

If we have gx, to get Fx, we need to integrate from 0 to x. Am I right?

So to get gx from Fx, we need to find the derivative, because it's an opposite operation from integration.

g(x) = dF/dx.

By the way, your definition of F(x) is very incomplete, you should have included the values of x for which the given rule applies. As it happens, I doubt very much that what you posted defines a valid cdf.
• Apr 16th 2011, 11:30 PM
Nforce
yes i have forgot; the interval is [250,1250]

I don't completely understand this:

g(x) = dF/dx.

What is dF in here? Do you mean the derivative? Can you solve for example above.
• Apr 17th 2011, 02:45 AM
mr fantastic
Quote:

Originally Posted by Nforce
yes i have forgot; the interval is [250,1250]

I don't completely understand this:

g(x) = dF/dx.

What is dF in here? Do you mean the derivative? Can you solve for example above.

Of course it's the derivative. What else could it possibly be?

I have no intention of solving it. Surely you know how to find the derivative of a function.
• Apr 17th 2011, 03:20 AM
Nforce
ok, thank you.