Sum digits after vpa(N,100) ?
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Hi MatLab!
I've stumbled across a problem. I wish to take all the first hundred digits in the square root of 2 ---> sqrt(2) and sum them up.
I first use
N=sym('sqrt(2)'); vpa(N,100)
which gives me alot of digits. But when I try to num2str the answer it cant be done. How can I achieve this?
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Shashank Prasanna
am 16 Jan. 2013
Here you go:
clear all
digits(100);
N=vpa(sym('sqrt(2)'));
sumA = 0;
for i = 1:100
sumA = sumA + (floor(N*(10^(i-1))) - 10*floor(N*10^(i-2)));
end
disp(sumA)
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Weitere Antworten (1)
Jan
am 16 Jan. 2013
Bearbeitet: Jan
am 16 Jan. 2013
Could you operate on the VPA number instead of converting it to a string? I do not have the Symbolic Toolbox, but I guess:
s = 0;
x = vpa(N, 100);
for ii = 1:100
s = s + floor(x);
x = rem(x, 1) * 10;
end
Does this work?
[EDITED]
N = sym('sqrt(2)');
x = vpa(N, 100);
s = 0;
for ii = 1:100
f = floor(x);
s = s + f;
x = (x - f) * 10;
end
If rounding error appear, try it with 200 digits in the VPA command. Please use this as inspiration - as I said already, I do not have the corresponding toolboxes.
5 Kommentare
Jan
am 16 Jan. 2013
Bearbeitet: Jan
am 16 Jan. 2013
Then let's debug your algorithm:
x = 1.414213562373095...
-> iteration starts
x = x*10-floor(x)*10
= 14.14213... - 1 * 10
= 4.14...;
s = s + 4;
Does the 1 not matter? And why do the loop stop at 99, when you need 100 elements?
Another test:
S = ['1.41421356237309504880168872420969807856967187537694807', ...
'3176679737990732478462107038850387534327641572735013846', ...
'230912297024924836055850737212644121497099935831'];
D = S - '0';
sum(D(3:102))
Jan
am 16 Jan. 2013
Now I can run Matlab again. The [EDITED] version works and gives the correct result.
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