Slicing Power Spectral Density over frequency bands

Question

I am using pwelch to get the Power Spectral Density of multiple signal vectors and then finding the average signal to noise ratios over 5 frequency bands.

I converted the power spectral densities to dB and am currently obtaining each band one by one:

P_signal1(band1)
P_signal1(band2)
P_signal1(band3)

...

P_signal2(band1)
P_signal2(band2)

and so on.

Is there any way to obtain this easily, maybe using arrays of the signals and the bands

signals = [P_signal1, P_signal2, P_signal3, P_signal4, P_signal5]
bands = [band1, band2, band3, band4, band5]

and obtain a matrix of each combination?

Answer 1

A = 1:100;
bands = [1:20;21:40;41:60;61:80;81:100];
A(bands)

Full documentation can be seen here .

The idea is indexing in Matlab is a lot different than in other languages, since Matlab uses matrices. When you index an array like A(1) , it will pick one element out, just like any other language. When you index it as A([2,1;3,1]) , magic happens. Matlab will take out elements of A 4 times, each corresponding to one element in [2,1;3,1] . And then it arranges the 4 results in the same form of [2,1;3,1] . The output will be also a matrix.

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EDIT: Using cell array

A = 1:100;
bands = {1:20;21:40;41:60;61:80;81:100};
cell2mat( cellfun(@(x) A(x), bands, 'UniformOutput', false) )

This works differently than above, but shares similar idea. Now bands is a cell array, each element containing an index range.

cellfun takes each of this range as x , and evaluate expression A(x) (which means access that part of A ), and put the result into a new cell array, of which the size is same with bands , and the element position accords to the definition in bands .

cell2mat converts this output cell array into a plain numeric array.