Factorial using a for loop

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Joseph
Joseph 2023-4-14
评论： John D'Errico 2023-4-14
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

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回答（2 个）

Walter Roberson
Walter Roberson 2023-4-14
编辑：Walter Roberson 2023-4-14
Ran in:
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.
Les Beckham
Les Beckham 2023-4-14
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
  2 个评论
Les Beckham
Les Beckham 2023-4-14
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
John D'Errico 2023-4-14
Ran in:
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.

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