Thread Subject: finding minium pts in a matrix

I have a matrix with 5 columns and n rows. I want to find
the minium number in column B before the numbers become
negative. Then I want to find the corresponding value in
the matrix in column D & E at the last positive number in
column B. How can I do this?

--Ender--

In article <g58aa8$lqr$1@fred.mathworks.com>, Ender <jr147@msstate.edu> wrote:
>I have a matrix with 5 columns and n rows. I want to find
>the minium number in column B before the numbers become
>negative. Then I want to find the corresponding value in
>the matrix in column D & E at the last positive number in
>column B. How can I do this?

What if the first number in the column is already negative?
What if the last positive number in column B is after the
numbers in that column went negative for awhile?
What if the last non-negative number in the column is 0? Then
does that 0 count as "the last positive number"?


minBeforeFirstNeg = min(Matrix(find(Matrix(:,2)<0,1)-1,2);
colsDEatLastPositive = Matrix(find(Matrix(:,2)>0,1,'last'),[4 5]);

In some combinations of circumstances the above can be optimized
a little; it depends on your answers to the questions.
--
  "Why does he stagger his mind with the mathematics of the sky?
  Once the question mark has arisen in the human brain the answer must
  be found, if it takes a hundred years. A thousand years."
                                              -- Walter Reisch

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
message <g58bbf$b8p$1@canopus.cc.umanitoba.ca>...
> In article <g58aa8$lqr$1@fred.mathworks.com>, Ender
<jr147@msstate.edu> wrote:
> >I have a matrix with 5 columns and n rows. I want to
find
> >the minium number in column B before the numbers become
> >negative. Then I want to find the corresponding value
in
> >the matrix in column D & E at the last positive number
in
> >column B. How can I do this?
>
> > What if the last positive number in column B is after
the
> numbers in that column went negative for awhile?
> What if the last non-negative number in the column is 0?
Then
> does that 0 count as "the last positive number"?
>
>
> minBeforeFirstNeg = min(Matrix(find(Matrix(:,2)<0,1)-
1,2);
> colsDEatLastPositive = Matrix(find(Matrix(:,2)
>0,1,'last'),[4 5]);
>
> In some combinations of circumstances the above can be
optimized
> a little; it depends on your answers to the questions.
> --
> "Why does he stagger his mind with the mathematics of
the sky?
> Once the question mark has arisen in the human brain
the answer must
> be found, if it takes a hundred years. A thousand
years."
> -- Walter
Reisch


To answer your question:

"What if the first number in the column is already
negative?"

This is not possible because I have graphed the data. The
graph moves through 0 in the x-axis then has a negative
minimum point then goes back through 0 again (x-axis).

"What if the last positive number in column B is after the
numbers in that column went negative for awhile?"

This does happen, but I am only interested in the instant
when the data first becomes 0.


What if the last non-negative number in the column is 0?
Then does that 0 count as "the last positive number"?

The data will never be exactly 0. I want the last positive
number before the data becomes negative.


I think this will help narrow down my search criteria.

--Ender--

In article <g58e4n$141$1@fred.mathworks.com>, Ender <jr147@msstate.edu> wrote:
>roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
>message <g58bbf$b8p$1@canopus.cc.umanitoba.ca>...
>> In article <g58aa8$lqr$1@fred.mathworks.com>, Ender
><jr147@msstate.edu> wrote:
>> >I have a matrix with 5 columns and n rows. I want to
>find
>> >the minium number in column B before the numbers become
>> >negative. Then I want to find the corresponding value
>in
>> >the matrix in column D & E at the last positive number
>in
>> >column B. How can I do this?


>"What if the last positive number in column B is after the
>numbers in that column went negative for awhile?"

>This does happen, but I am only interested in the instant
>when the data first becomes 0.


Okay, then, a small modification of what I had before:

OLD:
minBeforeFirstNeg = min(Matrix(find(Matrix(:,2)<0,1)-1,2);
colsDEatLastPositive = Matrix(find(Matrix(:,2)>0,1,'last'),[4 5]);

NEW:

numLeadingNonneg = find( Matrix(:,2)<0, 1) - 1;
minBBeforeFirstNeg = min( Matrix(1:numLeadingNonneg,2) );
colsDEatLastPositive = Matrix(minBBeforeFirstNeg,[4 5]);

--
  "Do not wait for leaders. Do it alone, person to person."
                                              -- Mother Teresa

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
message <g58fj7$hdv$1@canopus.cc.umanitoba.ca>...
> In article <g58e4n$141$1@fred.mathworks.com>, Ender
<jr147@msstate.edu> wrote:
> >roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
> >message <g58bbf$b8p$1@canopus.cc.umanitoba.ca>...
> >> In article <g58aa8$lqr$1@fred.mathworks.com>, Ender
> ><jr147@msstate.edu> wrote:
> >> >I have a matrix with 5 columns and n rows. I want to
> >find
> >> >the minium number in column B before the numbers
become
> >> >negative. Then I want to find the corresponding
value
> >in
> >> >the matrix in column D & E at the last positive
number
> >in
> >> >column B. How can I do this?
>
>
> >"What if the last positive number in column B is after
the
> >numbers in that column went negative for awhile?"
>
> >This does happen, but I am only interested in the
instant
> >when the data first becomes 0.
>
>
> Okay, then, a small modification of what I had before:
>
> OLD:
> minBeforeFirstNeg = min(Matrix(find(Matrix(:,2)<0,1)-
1,2);
> colsDEatLastPositive = Matrix(find(Matrix(:,2)
>0,1,'last'),[4 5]);
>
> NEW:
>
> numLeadingNonneg = find( Matrix(:,2)<0, 1) - 1;
> minBBeforeFirstNeg = min( Matrix(1:numLeadingNonneg,2) );
> colsDEatLastPositive = Matrix(minBBeforeFirstNeg,[4 5]);
>
> --
> "Do not wait for leaders. Do it alone, person to
person."
> -- Mother
Teresa



I am having trouble with the code. I put in the code you
suggested, but here is the error that I am getting. I am
not really sure what it means:

??? Subscript indices must either be real positive
integers or logicals.

Error in ==> Electric_Constants at 55
colsDEatLastPositive = JackR(minBBeforeFirstNeg,[4 5]);


--Ender--

In article <g5fqrm$dbo$1@fred.mathworks.com>, Ender <jr147@msstate.edu> wrote:
>roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
>message <g58fj7$hdv$1@canopus.cc.umanitoba.ca>...

>> numLeadingNonneg = find( Matrix(:,2)<0, 1) - 1;
>> minBBeforeFirstNeg = min( Matrix(1:numLeadingNonneg,2) );
>> colsDEatLastPositive = Matrix(minBBeforeFirstNeg,[4 5]);

>??? Subscript indices must either be real positive
>integers or logicals.

Opps, correction to my correction:

numLeadingNonneg = find( Matrix(:,2)<0, 1) - 1;
minBBeforeFirstNeg = min( Matrix(1:numLeadingNonneg,2) );
lastPosBeforeFirstNeg = find(Matrix(1:numLeadingNonneg,2)>0,1,'last');
colsDEatLastPositive = Matrix(lastPosBeforeFirstNeg,[4 5]);

--
  "To the modern spirt nothing is, or can be rightly known,
  except relatively and under conditions." -- Walter Pater