Precision of num2str function

I try to make o PRNG using the middle square method.

When I come the the point where I need to keep the middle digits of a number. I convert from double to string.

The precision is set in the function as 8. But after 70 iterations it does not have the the desired precision when converting from double to string.

The code can be seen bellow.

format long
seed=2315;
m=256;
z(1)=seed;
for i=2:m
    z(i-1)=z(i-1)^2;
    u(i-1)=z(i-1)/(10^(2*4));
    t=convertStringsToChars(num2str(u(i-1),8));
    temp=t(5:8);
    temp=str2double(temp);
    z(i)=temp;
end

For example when i=69 u(i-1)=0.06270016 and when it converts to string and then char it becomes '0.06270016'

And when i=70 u(i-1)=0.07290000 but this becomes '0.0729'.

How can I make it be '0.07290000' after the conversion?

Answer 1

[Stephen23]

If you want that much control over the text format then you should be using SPRINTF.

But in lieu of that, you can specify the format string with NUM2STR:

num2str(0.06270016,'%.8f')

ans = '0.06270016'

num2str(0.0729,'%.8f')

ans = '0.07290000'

[Panagiotis Artemiou]

Thank you very much. This was really helpful!