Thread Subject: Problem with Indexing!

I've a problem with finding the index in a single vector.
i've calculated some parameters for a document for some
values of theta ranging from -15 to +15 in steps of 5. that
means

1col -15
2col -10
3col -5
4col 0
5col 5
6col 10
7col 15

i find the maximum value out of these, but i dunno how to
get back the angle correspondingly using the positive matrix
indices. i.e., if the column number i get is 3rd, how do
calculate the actual -5?

Hi Arch,

maybe the function "find" will help you, but I don't
understand what you mean. Which variables do you have?
Could you please give an example?

Uwe

Arch <archforgroups@gmail.com> wrote in message <cb0a6834-
76ba-4437-8ff5-1e9937ad1e66@x1g2000prh.googlegroups.com>...
> I've a problem with finding the index in a single vector.
> i've calculated some parameters for a document for some
> values of theta ranging from -15 to +15 in steps of 5.
that
> means
>
> 1col -15
> 2col -10
> 3col -5
> 4col 0
> 5col 5
> 6col 10
> 7col 15
>
> i find the maximum value out of these, but i dunno how to
> get back the angle correspondingly using the positive
matrix
> indices. i.e., if the column number i get is 3rd, how do
> calculate the actual -5?

Thanks for responding.

Well, see i've some values in an array

Index Value
1 67
2 34
3 211
4 150
5 62
6 58
7 56

Now the indices are some counts. but the parameters are
calculated for some values of theta ranging from -15 to 15
in steps of 5. so 1 will correspond to calculation for theta
= -15. how do i retain the actual values - cos we can't
index arrays using negative indices!


"Uwe Steinmann" <uwe_steinmann@web.de> wrote in message
<g28fo6$fua$1@fred.mathworks.com>...
> Hi Arch,
>
> maybe the function "find" will help you, but I don't
> understand what you mean. Which variables do you have?
> Could you please give an example?
>
> Uwe
>
> Arch <archforgroups@gmail.com> wrote in message <cb0a6834-
> 76ba-4437-8ff5-1e9937ad1e66@x1g2000prh.googlegroups.com>...
> > I've a problem with finding the index in a single vector.
> > i've calculated some parameters for a document for some
> > values of theta ranging from -15 to +15 in steps of 5.
> that
> > means
> >
> > 1col -15
> > 2col -10
> > 3col -5
> > 4col 0
> > 5col 5
> > 6col 10
> > 7col 15
> >
> > i find the maximum value out of these, but i dunno how to
> > get back the angle correspondingly using the positive
> matrix
> > indices. i.e., if the column number i get is 3rd, how do
> > calculate the actual -5?
>

Hi Archana,

I'm not sure this is what you mean, but try this:

phi = -15:5:15;
vec = [67 34 211 150 62 58 56];
[M ind] = max(vec);
whatYouAreLookingFor = phi(ind);

Hoop it helped, and welcome to matlab :)

"Archana Ananthanarayan" <archana1985_ms@hotmail.com> wrote
in message <g28gat$qe8$1@fred.mathworks.com>...
> Thanks for responding.
>
> Well, see i've some values in an array
>
> Index Value
> 1 67
> 2 34
> 3 211
> 4 150
> 5 62
> 6 58
> 7 56
>
> Now the indices are some counts. but the parameters are
> calculated for some values of theta ranging from -15 to 15
> in steps of 5. so 1 will correspond to calculation for theta
> = -15. how do i retain the actual values - cos we can't
> index arrays using negative indices!
>
>
> "Uwe Steinmann" <uwe_steinmann@web.de> wrote in message
> <g28fo6$fua$1@fred.mathworks.com>...
> > Hi Arch,
> >
> > maybe the function "find" will help you, but I don't
> > understand what you mean. Which variables do you have?
> > Could you please give an example?
> >
> > Uwe
> >
> > Arch <archforgroups@gmail.com> wrote in message <cb0a6834-
> > 76ba-4437-8ff5-1e9937ad1e66@x1g2000prh.googlegroups.com>...
> > > I've a problem with finding the index in a single vector.
> > > i've calculated some parameters for a document for some
> > > values of theta ranging from -15 to +15 in steps of 5.
> > that
> > > means
> > >
> > > 1col -15
> > > 2col -10
> > > 3col -5
> > > 4col 0
> > > 5col 5
> > > 6col 10
> > > 7col 15
> > >
> > > i find the maximum value out of these, but i dunno how to
> > > get back the angle correspondingly using the positive
> > matrix
> > > indices. i.e., if the column number i get is 3rd, how do
> > > calculate the actual -5?
> >
>

Thanks a ton. It helped :)



"Yonathan Nativ" <yonathan_n_REMOVE-THIS@hotmail.com> wrote
in message <g28h56$lki$1@fred.mathworks.com>...
> Hi Archana,
>
> I'm not sure this is what you mean, but try this:
>
> phi = -15:5:15;
> vec = [67 34 211 150 62 58 56];
> [M ind] = max(vec);
> whatYouAreLookingFor = phi(ind);
>
> Hoop it helped, and welcome to matlab :)
>
> "Archana Ananthanarayan" <archana1985_ms@hotmail.com> wrote
> in message <g28gat$qe8$1@fred.mathworks.com>...
> > Thanks for responding.
> >
> > Well, see i've some values in an array
> >
> > Index Value
> > 1 67
> > 2 34
> > 3 211
> > 4 150
> > 5 62
> > 6 58
> > 7 56
> >
> > Now the indices are some counts. but the parameters are
> > calculated for some values of theta ranging from -15 to 15
> > in steps of 5. so 1 will correspond to calculation for theta
> > = -15. how do i retain the actual values - cos we can't
> > index arrays using negative indices!
> >
> >
> > "Uwe Steinmann" <uwe_steinmann@web.de> wrote in message
> > <g28fo6$fua$1@fred.mathworks.com>...
> > > Hi Arch,
> > >
> > > maybe the function "find" will help you, but I don't
> > > understand what you mean. Which variables do you have?
> > > Could you please give an example?
> > >
> > > Uwe
> > >
> > > Arch <archforgroups@gmail.com> wrote in message <cb0a6834-
> > >
76ba-4437-8ff5-1e9937ad1e66@x1g2000prh.googlegroups.com>...
> > > > I've a problem with finding the index in a single
vector.
> > > > i've calculated some parameters for a document for some
> > > > values of theta ranging from -15 to +15 in steps of 5.
> > > that
> > > > means
> > > >
> > > > 1col -15
> > > > 2col -10
> > > > 3col -5
> > > > 4col 0
> > > > 5col 5
> > > > 6col 10
> > > > 7col 15
> > > >
> > > > i find the maximum value out of these, but i dunno
how to
> > > > get back the angle correspondingly using the positive
> > > matrix
> > > > indices. i.e., if the column number i get is 3rd, how do
> > > > calculate the actual -5?
> > >
> >
>

"Archana Ananthanarayan" <archana1985_ms@hotmail.com> wrote in message
news:g28gat$qe8$1@fred.mathworks.com...
> Thanks for responding.
>
> Well, see i've some values in an array
>
> Index Value
> 1 67
> 2 34
> 3 211
> 4 150
> 5 62
> 6 58
> 7 56
>
> Now the indices are some counts. but the parameters are
> calculated for some values of theta ranging from -15 to 15
> in steps of 5. so 1 will correspond to calculation for theta
> = -15. how do i retain the actual values - cos we can't
> index arrays using negative indices!

So you have:

index = (1:7).';
value = [67; 34; 211; 150; 62; 58; 56];
theta = (-15:5:15).';

To find the maximum value and its location in the value matrix, use:

[maxValue, maxValueLocation] = max(value);

You can then use maxValueLocation to locate the elements of index and theta
in the same position as the maxValue is in the value matrix:

maxIndex = index(maxValueLocation);
maxTheta = theta(maxValueLocation);

Note that if index and value were combined in one matrix:

indexAndValue = [index value];

you can still do this by indexing into the columns of indexAndValue in your
MAX call:

[maxValue, maxValueLocation] = max(indexAndValue(:, 2));
maxIndex = indexAndValue(maxValueLocation, 1);
maxTheta = theta(maxValueLocation);

--
Steve Lord
slord@mathworks.com