if statement problem

Hello, I'm having some problems with an if statement. This is what I want to do: If x>1 A=B elseif x<1 and x>0.1 A=C elseif x<0.1 and x>0.01 A=D elseif x<0.001 A=F

I don,t seam to be able to get this working. Any help is welcome

Here is the code:

Y=random('unif',0.01,2,100,1);

for i=1:100

    if Y(1:i,1)>=1
        c(i,1)=1;
        c(i,2)=0; 
        c(i,3)=0;
    elseif (Y(1:i,1) < 1) && (Y(1:i,1) >= 0.1)
        c(i,1)=1;
        c(i,2)=0.5;
        c(i,3)=0; 
    elseif (Y(1:i,1)<0.1) && (Y(1:i,1)>=0.01)
        c(i,1)=1;
        c(i,2)=1;
        c(i,3)=0;
    elseif Y(1:i,1)<0.01 
        c(i,1)=0;
        c(i,2)=1;
        c(i,3)=0;
    end
end

Answer 1

[Oleg Komarov]

You should use:

Y(i,1)

instead of

Y(1:i,1)

Also preallocate c:

c = zeros(size(Y,1),3);

You can simply write:

if Y(i,1) < 0.01
    ...
elseif Y(i,1) < 0.1
    ...
elseif Y(i,1) < 1
    ...
else
    ...
end

[Hugo Policarpo]

Thanks,

the ":" where the problem.

solved

Answer 2

[Sean de Wolski]

    if Y(1:i,1)>=1

let's say

Y = [0 1 2 3]' ;
for i = 1:4

    if Y(1:i,1)>=1
        disp('yup');
    else
        disp('nope');
    end
  end

What do you see?

All nopes, the way MATLAB is interpreting this is

 if(all(Y(1:i,1))>1)

• when i = 1,( Y(1:1,1) = 0 )> 1) nope
• when i = 2, Y(1:2,1) = [0 1] > 1, are both of them? nope
• when i = 3, Y(1:3,1) = [0 1 2] > 1, are all of them? nope

I think you probably want to change your if statement to Y(i,1) also look at

doc any
doc all

for more information

Answer 3

[Jan]

Some of the check are redundant: If the Y(i,1)>=1 check is FALSE, you do not have to check for Y(i,1)<1 again:

Y = random('unif',0.01,2,100,1);
c = zeros(100, 3);   % Pre-allocation!!!
for i = 1:100
  if Y(i,1) >= 1
      c(i,1)=1;
      % c(i,2)=0;  % Set already 
  elseif Y(i,1) >= 0.1
      c(i,1)=1;
      c(i,2)=0.5;
  elseif Y(i,1) >= 0.01
      c(i,1)=1;
      c(i,2)=1;
  else
      % c(i,1)=0;  % Set already
      c(i,2)=1;
  end
end

c(i,3) is set to 0 in all cases. Then it is cheaper to set the default value in the pre-allocation accordingly.

[Hugo Policarpo]

Thanks