iterating a loop many times

• I'm not sure how to iterate this loop 1,000 times:
• ---a=randperm(20)
• LOOP STARTS:
• --- code that swaps 2 elements in 'a' randomly to make a guess 'amaybe'
• --- if fun(amaybe)>fun(a)
• anew=amaybe; (guess is kept)
• elseif fun(amaybe)<fun(a)
• anew=a; (guess is rejected)
• end
• LOOP ENDS

I need to make 1,000 guesses (swapping 2 elements each time) until the final guess should have the highest fun value. How do I iterate the loop that many times? And should I use a for-loop instead of if/elseif?

Answer 1

[Star Strider]

I would use a for loop because (1) it seems you need to do 1000 iterations and (2) the comparison operation (whatever it is that ‘fun’ does) doesn’t affect the number of iterations.

[Erik Lee]

Could you walk me through the syntax for iterating a for-loop for x amount of times? I also need to include the swapping code, but it's not a part of the for-loop. And for the for-loop, I used a nested variety, but idk if that works:

• for fun(amaybe)>fun(a)
• anew=amaybe;
• for fun(amaybe)<fun(a)
• anew=a;
• end
• end

[Star Strider]

Sure. You just tell it the number of times to iterate:

for k1 = 1:1000
    ... DO STUFF ...
end

You need to replace your for statements (that are incorrect) with if blocks:

if fun(amaybe)>fun(a)
    anew=amaybe;
e1seif fun(amaybe)<fun(a)
    anew=a;
end

The if block will work, providing ‘fun’ returns a scalar.

[Erik Lee]

Thanks, you're a total lifesaver for a coding noob like me :)

[Star Strider]

As always, my pleasure!