Factorial using a for loop

I need to write a for loop that calculates the factorial 100

This is the code that I have written. I now need to display the value of 100! and asign it to the variable nf

How could I go about that?

n=100
x=1
for b=1:n 
     x=x*b
end

Answer 1

[Walter Roberson]

n=75;
x=sym(1);
for b=1:n 
     x=x*b;
end

nf_sym = x

nf_sym = 

24809140811395398091946477116594033660926243886570122837795894512655842677572867409443815424000000000000000000

You will not be able to calculate this accurately using double precision.

format long g
n=75;
x=(1);
for b=1:n 
     x=x*b;
end

nf = x

nf = 
     2.48091408113954e+109

double(nf_sym) - nf

ans = 
      8.34369935906606e+93

That is, the final digits in the pure double precision calculation are not correct compared to calculating exactly and taking double precision afterwards.

Answer 2

[Les Beckham]

Your code works fine (though I would add semicolons to the end of all lines except the for and end to avoid spewing a bunch of stuff to the command window).

Then add this after your existing code to "assign it to the variable nf". Or, you could just replace the x variable with nf.

nf = x

[Les Beckham]

Also, if you are just getting started with Matlab, I would highly recommend that you take a couple of hours to go through the free online tutorial: Matlab Onramp

[John D'Errico]

All correct. I would add however, that factorial(100) is NOT representable exactly as a double precision number.

factorial(100)

ans = 9.3326e+157

So only the first 16 decimal digits of that result will be correct.