Combining matrices

Question

Paul 2011-11-9

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编辑： Paul 2015-12-2

I'm trying to build a matrix with the number of occurences of a given condition from two matrices.

The objective is to now the number of points that correspond to a given statement and combining this into a m*n matrix to use on a plot

For example: how many waves have period<0.5 and height<1, how many waves have period<0.5 and 1<height<1.5. etc...

my class intervals are period=[0:1:17] and height=[0:0.5:10].

Is there a way to build a function that would in some way combine the two classes into a matrix that would help me build something like (I'm only interested in the numbers):

http://i1228.photobucket.com/albums/ee441/Elcook/Picture1-1.jpg

t=[period H] x=matrix size(t) %with the number of occurences of each class.

I tried using multiple for and if conditions and even simpler ways, but I'm feeling really lost.

Can someone help me?

thank you in advance

Paul

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Answer 1

Paul 2011-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/20764-combining-matrices#answer_27445

Basically, I want to do something like:

intervalHs=[0:0.5:10];

intervalTe=[0:1:20];

a=sum((Hs>0.5)&(Hs<1)&(Te<=1))

b=sum((Hs>2)&(Hs<=2.5)&(Te<=6)&(Te>5))

x=sum((Hs<=0.5)&(Te<=1))

y=sum((Hs<=0.5)&(Te>1)&(Te<=2))

z=sum((Hs<=0.5)&(Te>2)&(Te<=3))

and the construct a matrix (m*n) with the results

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Answer 2

John Petersen 2011-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/20764-combining-matrices#answer_27418

Paul, Try find() or a straight comparison (if you don't need to know the indices). For example,

function [num_periods, num_heights] = findnum(period,plowvalue,phighvalue,height,hlowvalue,hhighvalue)

num_periods = sum((period>plowvalue)&(period<phighvalue));

num_heights = sum((height>hlowvalue)&(height<hhighvalue));

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Paul 2011-11-9

First, thanks for the answer.

I did tried to do something like that. Unfortunately that would mean I would have to insert all the possible combinations between the two classes one by one.

The idea is to count the number of waves that fall into both classes at once for each class interval (I'm finding some trouble in explaining).

For example: in the figure the value that corresponds to the number of waves that have a period between 5 and 6 s and a height between 1.5 and 2 is 584.

I know there must be a easy way of doing so, but I can't put my finger on it!

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Answer 3

Paul 2015-12-2

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https://ww2.mathworks.cn/matlabcentral/answers/20764-combining-matrices#answer_201960

编辑：Paul 2015-12-2

在 MATLAB Online 中打开

THIS IS THE ACCEPTED ANSWER!!!!!!!!!!!!!!!!

I can't seem to undo my previou accepted answer....

y=0:1:20; %Te interval
x=0:0.5:10; %Hs interval
Hs=seccao1(:,2);
Tm=seccao1(:,3);
for n=1:20
       Tm_id=Tm(Hs>x(n) & Hs<=x(n+1));
           for k=1:20
               s=sum(Tm_id>y(k) & Tm_id<=y(k+1));
              M(n,k)=s;  % M is a matrix with the number of occurences of each given interval (i.e: number of waves with                             %1<=Hs <1.5   and 5<=Te<6)
           end
  end