Thread Subject: matrix manipulation-maximum value

Hi all. I have a very simple matrix A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6 8;7 9;8 10;9 3;10 13].
As you can see the first column values are always growing. My objective is to compute the maximum value in the second column that corresponds to the range 3.5 to 7.2 in the first column. In this case matlab should only consider the sub matrix [4 0.5;5 7;6 8;7 9] and the final result should be 9. Is this possible to do in matlab?Many thanks.

"antonio ferreira" wrote in message <ip1o5p$28p$1@fred.mathworks.com>...
> Hi all. I have a very simple matrix A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6 8;7 9;8 10;9 3;10 13].
> As you can see the first column values are always growing. My objective is to compute the maximum value in the second column that corresponds to the range 3.5 to 7.2 in the first column. In this case matlab should only consider the sub matrix [4 0.5;5 7;6 8;7 9] and the final result should be 9. Is this possible to do in matlab?Many thanks.
- - - - - - - - -
max(A((3.5<=A(:,1))&(A(:,1)<=7.2),2))

Roger Stafford

On 4/24/2011 12:55 PM, antonio ferreira wrote:
> Hi all. I have a very simple matrix A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6
> 8;7 9;8 10;9 3;10 13].
> As you can see the first column values are always growing.

...red herring...like the superfluous information in the elementary
mathbook.


My objective
> is to compute the maximum value in the second column that corresponds to
> the range 3.5 to 7.2 in the first column. In this case matlab should
> only consider the sub matrix [4 0.5;5 7;6 8;7 9] and the final result
> should be 9. Is this possible to do in matlab?

Of course...

Solution in steps for pedagogical purposes....look up "logical
addressing" in "Getting Started" section for particulars.

 >> A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6 8;7 9;8 10;9 3;10 13];
 >> xmin=3.5;xmax=7.2;
 >> A(:,1)>=xmin & A(:,1)<=xmax
ans =
      0
      0
      0
      0
      1
      1
      1
      1
      0
      0
      0
 >> A(A(:,1)>=xmin & A(:,1)<=xmax,2)
ans =
     0.5000
     7.0000
     8.0000
     9.0000
 >> max(A(A(:,1)>=xmin & A(:,1)<=xmax,2))
ans =
      9
 >>

--

dpb <none@non.net> wrote in message <ip1q7d$smv$1@speranza.aioe.org>...
> On 4/24/2011 12:55 PM, antonio ferreira wrote:
> > Hi all. I have a very simple matrix A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6
> > 8;7 9;8 10;9 3;10 13].
> > As you can see the first column values are always growing.
>
> ...red herring...like the superfluous information in the elementary
> mathbook.
>
>
> My objective
> > is to compute the maximum value in the second column that corresponds to
> > the range 3.5 to 7.2 in the first column. In this case matlab should
> > only consider the sub matrix [4 0.5;5 7;6 8;7 9] and the final result
> > should be 9. Is this possible to do in matlab?
>
> Of course...
>
> Solution in steps for pedagogical purposes....look up "logical
> addressing" in "Getting Started" section for particulars.
>
> >> A=[0 0.5;1 3;2 4;3 1; 4 0.5;5 7;6 8;7 9;8 10;9 3;10 13];
> >> xmin=3.5;xmax=7.2;
> >> A(:,1)>=xmin & A(:,1)<=xmax
> ans =
> 0
> 0
> 0
> 0
> 1
> 1
> 1
> 1
> 0
> 0
> 0
> >> A(A(:,1)>=xmin & A(:,1)<=xmax,2)
> ans =
> 0.5000
> 7.0000
> 8.0000
> 9.0000
> >> max(A(A(:,1)>=xmin & A(:,1)<=xmax,2))
> ans =
> 9
> >>
>
> --
>

Right...thanks