How can i create an if-function with probability p ?

Hi, im quite new in all this, i hope someone can help me.

I should generate a function that with probability p calculates for example y=2x and with probability 1-p y = 5x. I don't know how to do it but i thought of creating a variable, lets call it C, that equals 1 with probability p and something else with p-1 or something similar and then create an if function with

    if C=1
    y=2x
    else 
    y=5x

But is there the possibility to create something like C and how? Or is there an easier way to do this?

Sorry, i hope this was clear and thanks in advance!

Best, Nina

[James Tursa]

Did you bother reading the answer that was already posted on the Newsgroup?

http://www.mathworks.com/matlabcentral/newsreader/view_thread/340618

[Nina Gerber]

thanks & sorry for bothering i haven't found the answer!

[Walter Roberson]

I confirm that Roger's solution works.

For example,

x = 1 : 10;
p = 0.2;
for tryno = 1 : 8
  if rand <= p
     y = 2 * x
  else
     y = 5 * x
  end
end

You can see that the answer is not always the same

Answer 1

[Roger Stafford]

   if rand<=p
     y = 2*x;
   else
     y = 5*x;
   end

[Nina Gerber]

Thanks, but If i run the function like this it always returns the else command, so y=5*x what im i doing wrong?

[Roger Stafford]

That would only be true if you reset the "seed" for 'rand' processing using 'rng' each time you called 'rand', or if you shut off the computer each time.