How to overwrite part of a matrix by a function of the row number.

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Emerson De Souza
Emerson De Souza 2011-4-18
I want to overwrite part of a matrix by a function of the row number.
For example, let
M=rand(10,5) and the function of row number:
f(ROW)=ROW^2.
This function should apply in the range from 1:5 for all columns.
Thus the overwritten matrix N would have the following components
1 1 1 1 1
4 4 4 4 4
9 9 9 9 9
16 16 16 16 16
25 25 25 25 25
0.0620452213196326 0.533771951767000 0.526102465795561 0.337583864052045 0.0513318861123711
0.298243971887764 0.109154212042459 0.729709448223228 0.607865907262946 0.0728852990989761
0.0463512648981808 0.825808857855598 0.707253485315422 0.741254049502218 0.0885274596747204
0.505428142457703 0.338097718802172 0.781377051799277 0.104813241973500 0.798350864113952
0.761425886690113 0.293973053026484 0.287976975614171 0.127888379782995 0.943008139570703
ONLY the initial 5 rows are changed by the power of row number
and ALL columns were modified likewise.
I tried the following approach:
M=rand(10,5);
r=1:1:5;
f=r'.^2;
M(1:5,:)=f;
but did not work.
I hope someone know how to correct this command or to suggest something new.
Thank your for your help
Emerson

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采纳的回答

Walter Roberson
Walter Roberson 2011-4-18
for r = 1:5
M(r,:) = r^2;
end

更多回答（1 个）

Andrei Bobrov
Andrei Bobrov 2011-4-18
without loop for
r = 1:5;
M(r,:) = r.'.^2*ones(1,size(M,2))
  1 个评论
Emerson De Souza
Emerson De Souza 2011-4-18
Thank you Andrei,
your suggestion is definitely valid in particular if a loop
is not desired.
Have a nice day
Emerson

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