if statement problem

13 次查看（过去 30 天）
Hugo Policarpo
Hugo Policarpo 2011-8-26
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

请先登录，再回答此问题。

采纳的回答

Oleg Komarov
Oleg Komarov 2011-8-26
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

更多回答（2 个）

Sean de Wolski
Sean de Wolski 2011-8-26
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
Jan
Jan 2011-8-26
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.

类别

在 Help Center 和 File Exchange 中查找有关 Creating, Deleting, and Querying Graphics Objects 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by