prime factor function matlab

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Daabir Momin
Daabir Momin 2023-4-2
回答： Dyuman Joshi 2023-4-3
function [z1] = pfact(Z)
if Z>=2
p = 2:Z;
q = mod(Z,p);
a=find(q==0);
z1=p(a)
elseif Z==1
z1 = 1
elseif Z==0
z1 = []
disp("error")
end
I'm trying to get only prime factors but this code gives me all the factors, I need the prime factors that when they multiply with each other they give the original number.
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Daabir Momin
Daabir Momin 2023-4-2
Z should be [2,2,5] , but I'm confused as to how I should approach the solution without using the factor function.
Daabir Momin
Daabir Momin 2023-4-2
function [z1] = pfact(Z)
if Z>=2
p = 2:Z;
q = mod(Z,p);
a=find(q==0);
z1=p(a)
elseif Z==1
z1 = 1
elseif Z==0
z1 = []
disp("error")
end
pfact(20)
This gives me all the factors, can someone help me manipulate this code so it gives only the prime factors that when mutiplied together it gives you the original number.
like 20 should give output of [2,2,5]

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回答（1 个）

Dyuman Joshi
Dyuman Joshi 2023-4-3
Ran in:
The code you wrote gives the divisors of Z.
This should work well unless you are dealing with extremely large numbers -
out1=pfact(20)
out1 = 1×3
2 2 5
out2=pfact(prod(primes(15)))
out2 = 1×6
2 3 5 7 11 13
function [z1] = pfact(Z)
if Z>=2
p = primes(sqrt(Z));
z1 = [];
while Z>1
d = p(rem(Z,p)==0);
if isempty(d)
z1=[z1 Z];break
end
z1=[z1 d];
Z = Z/prod(d);
end
z1=sort(z1);
elseif Z==1
z1 = 1;
elseif Z==0
z1 = [];
disp("error")
end
end

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