Returning peak values from a column

Hello,

I am trying to do the following. I have two column vectors:

 Cp=[0;0.4;0.8;0.99;0.8;0.4;0];

 Cf=[1;2;3;4;5;6;7];

I am trying to obtain a Cf column vector for the corresponding Cp column vector peak and below. So Cp peaks at 0.99 and I am trying to obtain the values for Cf from the beginning of Cp until the peak of Cp. All of the values of Cp are less than the peak value.

So

 Cf_new=[1;2;3;4]

I am also trying to obtain the last half of Cf for Cp after the peak until the end. So the last half would be:

 Cf_new2=[5;6;7]

Thank you

Answer 1

[Matt J]

 [~,idx]=max(Cp);
 Cf_new=Cf(1:idx);
 Cf_new2=Cf(idx+1:end);

Answer 2

[Image Analyst]

peakIndex = find(diff(Cp) < 0, 1, 'first')
Cf_new = Cf(1 : peakIndex)
Cf_new2 = Cf(peakIndex+1:end)

In the command window:

peakIndex =
     4
Cf_new =
     1
     2
     3
     4
Cf_new2 =
     5
     6
     7

Or you might mean "max value" instead of peak. In that case you need to use max() instead of diff(), and you need to know what you want to do if you have a run of several max values in a row.

[Christopher]

Thanks Image Analyst

Answer 3

[Andrei Bobrov]

t = [true;diff(Cp(:))>=0]
Cf_new = Cf(t);
Cf_new2 = Cf(~t);