change specific col and row in a matrix

Hi, let say i have matrix A=[20 40 60 70; 10 20 30 40; 60 50 20 10]. I want to change value in these location (e.g (2,2),(3,2),(1,4)) to 5 without having typing one by one to change the value.. how i can do that?

[Tiasa Ghosh]

do you have a pattern for the specific locations?

Answer 1

[KSSV]

A=[20 40 60 70; 10 20 30 40; 60 50 20 10] ;
r = [2 3 1] ;
c = [2 2 1] ;
B = A ;
% Method 1 , use loop
for i = 1:length(r)
    A(r(i),c(i)) = 5 ;
end

% Method 2, use indices
idx = sub2ind(size(A),r,c) ;
B(idx) = 5 ;

Answer 2

[Rita Barnabé]

Hi, how do I change all the values in a specific column ?

%Original values

ecg = Data (:,6);

n = 9;                 % Number of bits of the channel  (?)
VCC = 3;               % Operating voltage
Gecg = 1000;           % Sensor gain

ecg_volts = (ecg/(2^n)-1/2)*VCC/Gecg;

and now i want to change ecg to ecg_volts value

[Walter Roberson]

Data(:,6) = ecg_volts;