MATLAB: Repeating an index number n times in a vector

vector index number

Hi People,

I'd like to transform a vector p like this one. p=[3 0 2 2 1 0 3]

Into a new vector that has n times the indexnumber of n, for example:

new vector: v=[1 1 1 3 3 4 4 5 7 7 7] so it has 3 times 1, zero times 2, 2 times 3 and so on.

the numbers generated in p are variable but are always between 0 and 15

I hope you can help me.

Regards, Siem

Best Answer

v = [];
count = 1;
for j = 1:length(p) 
  if p(j) ~= 0
    v(count:count+p(j)-1) = j*ones(p(j),1);
    count = count + p(j);
  end
end

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MATLAB: Making matrix whose submatrices are from for loop

for j = 2:Jmax
  P{j-1}=(sqrt(-2*p(j-1)+1)/sqrt(-2*p(j-1)))*(I-(p(j)+p(j-1))*inv(A+p(j)*I))
  V{j}=P{j-1}*V{j-1};  
  W=[W V{j}]

It is not clear whether p (lower-case) is intended to be a matrix or a vector. If it is intended to be a matrix then

for j = 2:Jmax
  P{j-1}=(sqrt(-2*p{j-1}+1)/sqrt(-2*p{j-1}))*(I-(p{j}+p{j-1})*inv(A+p{j}*I))
  V{j}=P{j-1}*V{j-1};  
  W=[W V{j}]

Based upon the p(j)*I, my suspicion would be that p(j) is intended to be a scalar, but that is not certain.

MATLAB: Reverse indexing of a matrix in matlab

Hi Lilly,

You get error at that line, because, you just removed the sort operation, which can provide two outputs.

The code can not have two outputs, when it is just a variable and no operation is performed on it.

Your code above doesn't perform what you wanted to do. You can perform or get the inverse, with the help of Index variable.

Here is the code that can be done, if you have Index variable

P=[188 5 95 60;3 59 0 111;255 123 51 84 ];
Ma=[25 222 80 6;100 1 190 97;73 33 254 184 ];
M_1=zeros(size(Ma ));
P_1=zeros(size(P ));
Index = zeros(size(Ma));
for i=1:3
[M_1(i,:),Index(i,:)]=sort(Ma(i ,:));
P_1(i,:) = P(i,Index(i,:) );
end
%%%%%%Inverse
% Perform this with the help of Index
p_1 = zeros(size(P_1));
for j = 1:3
    p_1(j,Index(j,:)) = P_1(j,:);
end
p_1
isequal(p_1,P) % To check if p_1 is equal to P

Hope this helps.

Regards,

Sriram

Best Answer

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MATLAB: Making matrix whose submatrices are from for loop

MATLAB: Reverse indexing of a matrix in matlab

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