Multipling a multidimensinnal array with a vector
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John Hock
el 28 de Abr. de 2019
Comentada: Star Strider
el 1 de Mayo de 2019
Hi Everyone
I am trying to multiply a multidimensional 13*2560 (13 rows and 2560 coloumns) with 1*2560 (1 row and 2560 coloumns).
But matlab is giving error that matrix dimensions is nit match
For example as for simplest example
A=[1 2 3 4 ; 5 6 7 8]; 2*4 array
>> B=[11 22 33 44 ];1*4 vector
I want first row of A get multiplied with B and give its mean as a output then same for other row.
weighted_mean = mean(B.*A)
Please help
Thanks in advance
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Star Strider
el 28 de Abr. de 2019
Editada: Star Strider
el 28 de Abr. de 2019
If you want the mean of each row, specify the dimension argument as 2:
weighted_mean = mean(B.*A, 2);
That should do what you want.
EDIT —
To calculate a mean of the rows with respect to the elements of the weighting vector (as described in Mathematical definition (link) of the Weighted aritmentic mean), this works:
WeightedMean = sum(bsxfun(@times, B, A),2) / sum(B);
equivalently (R2016b and later releases):
WeightedMean = sum(B.*A,2) / sum(B);
This of course assumes that ‘B’ is the weighting vector.
Experiment to get the result you want.
6 comentarios
Star Strider
el 1 de Mayo de 2019
No worries.
If you want a (1 x 2562) result, sum down the columns rather than across the columns:
WeightedMean = sum(bsxfun(@times, abc, z3),1) / sum(abc);
or using the default column sum:
WeightedMean = sum(bsxfun(@times, abc, z3)) / sum(abc)
My only concern is that may not be the same thing as the true weighted mean, since you are applying the weighting vector across the columns, although summing down the columns.
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