[newbie] problem with for loop

[nukeymusic]

I'm trying to fill an array with the following script:
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end

this doesn't work however, the strange thing is when I don't use a for
loop but just enter lines one and two incrementing n myself each time
it I get the expected result

any help welcome (please don't shoot at a newbie)

nukeymusic

[Mario Baussmann]

try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end
this doesn't work however, the strange thing is when I don't use a for
loop but just enter lines one and two incrementing n myself each time
it I get the expected result
any help welcome (please don't shoot at a newbie)
nukeymusic

[nukeymusic]

Post by Mario Baussmann
try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end
this doesn't work however, the strange thing is when I don't use a for
loop but just enter lines one and two incrementing n myself each time
it I get the expected result
any help welcome (please don't shoot at a newbie)
nukeymusic

I tried that but the result is not OK as you can see from this (I put
the three lines in a file calc_series.m):
octave:1> calc_series
octave:2> x(1)
error: invalid matrix index = 1

I expected an array 1 2 2 3 3 3 4 4 4 4

I'm surely doing something wrong but what?


thanks for any help offered

nukeymusic

[Mirek]

Post by Mario Baussmann
try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end

n.*(n-1)./2+1 is greather then n.*(n-1)./2 then the result is
an empty range.

for n=1:5;disp(n.*(n-1)./2:n.*(n-1)./2+1);end

0 1
1 2
3 4
6 7
10 11

octave:2> x(1)
error: invalid matrix index = 1

because array x is empty :)

I expected an array 1 2 2 3 3 3 4 4 4 4

My solusion is:

octave:54> n=4;x=zeros(1,n*(n+1)/2),x(cumsum(0:n-1)+1)=1,x=cumsum(x)
x =

0 0 0 0 0 0 0 0 0 0

x =

1 1 0 1 0 0 1 0 0 0

x =

1 2 2 3 3 3 4 4 4 4

[nukeymusic]

On Jun 8, 4:54 pm, Mirek

Post by Mirek

Post by nukeymusic

Post by Mario Baussmann
try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end

n.*(n-1)./2+1 is greather then n.*(n-1)./2 then the result is
an empty range.

Oh dear, how stupid from me, it should have been:
x(n.*(n-1)./2+1:n.*(n+1)./2)=n;
after running the script like this x(1:10) contains the right numbers
The solution you offer below is probably better (less cpu-cycles?) for
large arrays
thanks a again for the help offered

nukeymusic

Post by Mirek
Reversing limits doesn't solve your problem:> for n=1:5;disp(n.*(n-1)./2:n.*(n-1)./2+1);end
0 1
1 2
3 4
6 7
10 11

Post by nukeymusic
octave:2> x(1)
error: invalid matrix index = 1

because array x is empty :)

Post by nukeymusic
I expected an array 1 2 2 3 3 3 4 4 4 4

octave:54> n=4;x=zeros(1,n*(n+1)/2),x(cumsum(0:n-1)+1)=1,x=cumsum(x)
x =
0 0 0 0 0 0 0 0 0 0
x =
1 1 0 1 0 0 1 0 0 0
x =
1 2 2 3 3 3 4 4 4 4

[nukeymusic]

On Jun 8, 4:54 pm, Mirek

Post by Mirek

Post by nukeymusic

Post by Mario Baussmann
try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end

n.*(n-1)./2+1 is greather then n.*(n-1)./2 then the result is
an empty range.
Reversing limits doesn't solve your problem:> for n=1:5;disp(n.*(n-1)./2:n.*(n-1)./2+1);end
0 1
1 2
3 4
6 7
10 11

Post by nukeymusic
octave:2> x(1)
error: invalid matrix index = 1

because array x is empty :)

Post by nukeymusic
I expected an array 1 2 2 3 3 3 4 4 4 4

octave:54> n=4;x=zeros(1,n*(n+1)/2),x(cumsum(0:n-1)+1)=1,x=cumsum(x)
x =
0 0 0 0 0 0 0 0 0 0
x =
1 1 0 1 0 0 1 0 0 0
x =
1 2 2 3 3 3 4 4 4 4

could you also tell how to make a function out of this (with n as a
parameter)?

thanks in advance
nukeymusic

[nukeymusic]

Post by nukeymusic
On Jun 8, 4:54 pm, Mirek

Post by Mirek

Post by nukeymusic

Post by Mario Baussmann
try: endfor instead of end ;-)
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end

n.*(n-1)./2+1 is greather then n.*(n-1)./2 then the result is
an empty range.
Reversing limits doesn't solve your problem:> for n=1:5;disp(n.*(n-1)./2:n.*(n-1)./2+1);end
0 1
1 2
3 4
6 7
10 11

Post by nukeymusic
octave:2> x(1)
error: invalid matrix index = 1

because array x is empty :)

Post by nukeymusic
I expected an array 1 2 2 3 3 3 4 4 4 4

octave:54> n=4;x=zeros(1,n*(n+1)/2),x(cumsum(0:n-1)+1)=1,x=cumsum(x)
x =
0 0 0 0 0 0 0 0 0 0
x =
1 1 0 1 0 0 1 0 0 0
x =
1 2 2 3 3 3 4 4 4 4

could you also tell how to make a function out of this (with n as a
parameter)?
thanks in advance
nukeymusic

I figured it out myself -though I'm not sure whether this is the best
practice-:

function answer = calc_sequence(k)
%calc_sequence
for n=1:k
x(n.*(n-1)./2+1:n.*(n+1)./2)=n;
endfor
answer = x(1:k);
endfunction

[Mario Baussmann]

.. and maybe you mean x(..,..) to adress the matrix
instead of x(..:..)?
Mario

Post by nukeymusic
clear
for n=1:10
x(n.*(n-1)./2+1:n.*(n-1)./2)=n;
end
this doesn't work however, the strange thing is when I don't use a for
loop but just enter lines one and two incrementing n myself each time
it I get the expected result
any help welcome (please don't shoot at a newbie)
nukeymusic