MATLAB Answers

Mate 2u

finding the location of the maximum of N periods

Asked by Mate 2u
on 26 Jul 2013

Hi all, I have prices of a financial time series in a matrix "Thai" of size "4048x1".

I want to create a new matrix of size 4048x1 full of zeros and 1s , where the 1 shows the maximum point within a n period in 4048. So for instance in 4048 prices, we check the first 200 prices for the maximum, then the next 200 prices find the maximum if n = 200.....and so on.


on 26 Jul 2013

Is this 'n' a sliding window or sequential?

Mate 2u
on 26 Jul 2013

erm....I think 1:200, 201:401, 401:601....etc

so lets say we have a 1000x1 matrix....we will have a 1000x1 matrix full of zeros with 5 1's and 995 0's, with the first 1 showing max location within 0:200, and so on.



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2 Answers

Answer by dpb
on 27 Jul 2013

OK, for "dead ahead" loop solution is fairly trivial--it didn't come to me otomh on vectorizing this owing to the indexing being inconsistent but there's bound to be a way; if the 'aha!' moment strikes I'll try to get back...

But, anyway...

function maxes=maxvec(x,N)
%   For vectors, maxvec(X,N) is a vector of same length as X 
%   containing the maximum value of X over groups of N elements 
%   returned in the position found in X.  
%   Not yet implemented for matrices.
if size(x,1)==1,error('X must be a column vector'), end
if numel(x)~=length(x),error('X must be a column vector'), end
if mod(L,N), error('Length of X not evenly divisible by N'), end
for i=1:N:L-N+1


Answer by Image Analyst
on 27 Jul 2013

The most "MATLAB-ish" way to do it is to use blockproc. Here's how to do it:

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
close all;
% Create data of prices with 2 places to the right of the decimal.
theSignal = fix(10000 * rand(1, 4048)) / 100;
% Now let's use an anonymous function.
% We'll take the max in the blocks.
windowSize = 200;
myFilterHandle = @(block_struct) ...
	max( * ones(size(;
% Find the max in each 200 element long block.
blockyMax = blockproc(theSignal, [1, windowSize], myFilterHandle);
[rowsM, columnsM, numberOfColorChannelsSD] = size(blockyMax);
% Plot it.
subplot(2, 1, 1);
plot(blockyMax, 'bo-');
caption = sprintf('Signal Processed in 1 by %d Blocks\n%d by %d pixels\nAnonymous Max Filter', ...
	windowSize, rowsM, columnsM);
title(caption, 'FontSize', fontSize);
% Find where the signal equals the block-wise max.
signalEqualMax = (theSignal == blockyMax);
% Plot it.
subplot(2, 1, 2);
plot(signalEqualMax, 'bo-');
title('1 where signal equals the max in a 200 long window', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);


on 27 Jul 2013


>> lookfor blk
>> lookfor block
slvblk                         - Solve almost block-diagonal linear system.
blockGetDialogSchema           - This is the default schema files for all SL blocks.
vipaviread                     - Read AVI file.  Used by Video & Image Processing Blockset's
ChkIfBlockReusable             - Checks whether Filter block is reusable
dspblkstructures               - Returns the structures supported by the Digital Filter Block.
isspblksinstalled              - Returns true if Simulink and Signal Processing Blockset are installed.
lnkfvtool2mask                 - Callback for linking FVTool to a block mask.
dfiltfftfirdemo                - Overlap-add FIR Block filter object

Maybe in some toolbox, not in base Matlab???

Image Analyst
on 28 Jul 2013

Oh, it's in the Image Processing Toolbox - I didn't realize that until now because so many people use it for non-imaging applications. In R2010b then changed the name from blkproc to blockproc.

on 28 Jul 2013

Ahhhh....not one included in what TMW kindly provided...

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