Optimization Simple search
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I got a quick question, lets say I have an array of numbers for example [ 9 3 2 7 1 8 ] and I want to find the minimum value ie: for this example it would be 1.
How could I implement an optimization search like this??
1 commentaire
Réponses (8)
John
le 20 Avr 2011
12 commentaires
Matt Fig
le 22 Avr 2011
I just noticed that my function incorrectly handles NaN's if the input has only NaN and Inf - the index is always 1. This must be part of the reason why MIN is so much slower with two outputs... It is doing some gymnastics when NaN's are encountered.
Matt Tearle
le 22 Avr 2011
Interesting! Thanks for the info. I did idly wonder if the number of outputs was making the difference, but couldn't see any reason why. Your explanation makes sense.
Paulo Silva
le 20 Avr 2011
m=[9 3 2 7 1 8 ]
%another way to find minimum value, using unique
u=unique(m);
u(1)
%another way to find minimum value, using sort
s=sort(m);
s(1)
%another way to find minimum value, a loop this time
MinVal=m(1);
for lo=1:numel(m)
if m(lo)<MinVal
MinVal=m(lo);
end
end
MinVal
1 commentaire
Andrei Bobrov
le 20 Avr 2011
or more loops for
k = sum(abs(m));
for jj = 1:numel(m)
k = min(k,m(jj));
end
Walter Roberson
le 20 Avr 2011
If you use one of the optimizers that do not require continuous derivatives, then for any x value, take K = floor(x); if that is out of the range 1:length(m) return +infinity, and otherwise return m(K)
The optimization routine should then find the minimum value, and floor() of the x value it returns will be the index of that value.
0 commentaires
John
le 21 Avr 2011
6 commentaires
Paulo Silva
le 21 Avr 2011
m=randi([1 10],5,2) %x and y array
MinVal=m(1,2);
MinValRow=1;
for lo=1:size(m,1)
if m(lo,2)<MinVal
MinVal=m(lo,2);
MinValRow=lo;
end
end
MinValy=MinVal
MinValx=m(MinValRow,1)
MinValRow
John
le 21 Avr 2011
1 commentaire
Paulo Silva
le 21 Avr 2011
even after being warned about the inefficiency of that method you insist on using it!
Your function does work fine:
m=randi([1 10],10,2) %x and y array
y=bubble(m(:,1),m(:,2))
y(1) %min value
Paulo Silva
le 21 Avr 2011
John code:
function y= bubble(x,y)
n = length(x);
for k = 1:n-1
for j = 1:n-k
if(x(j)> x(j+1))
temp = x(j);
x(j) = x(j+1);
x(j+1) = temp;
temp = y(j);
y(j) = y(j+1);
y(j+1) = temp;
end % if
end % for
end % for
y = x;
my code:
MinVal=m(1,2);
MinValRow=1;
for lo=1:size(m,1)
if m(lo,2)<MinVal
MinVal=m(lo,2);
MinValRow=lo;
end
end
Test with
n=1:2000
m=randi([1 10],n,2); %x and y array
You can see the time of code execution rising very fast with the bubble sort method, while with my code the time remains almost constant, better codes do exist and I bet that Matt Fig has better code :)
0 commentaires
John
le 22 Avr 2011
4 commentaires
Walter Roberson
le 22 Avr 2011
No, just a single pass through finding the minimum is *much* easier than sorting.
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