MATLAB: Returning negative value of element in vector

vector

Hi!

I need to return every second element in a vector as negative, how do I do it?

for example; v=[1 4 -0.3 0.2 4 7 14 -25 -0.003 245]

should be vnew=[1 -4 -0.3 -0.2 4 -7 14 25 -0.003 -245]

Best Answer

v=[1 4 -0.3 0.2 4 7 14 -25 -0.003 245];
v(2:2:end) = -v(2:2:end)

Result

>> v
v =
    1.0000   -4.0000   -0.3000   -0.2000    4.0000   -7.0000   14.0000   25.0000   -0.0030 -245.0000

Read about indexing in MATLAB: https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

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MATLAB: How to replace values in a matrix

Try a simple for loop:

A=[ 0.2 0.07 0.25 0.87 0.09 0.14 0.8 0.3;
  0.1 0.5 0.25 0.14 0.98 0.025 0.58 0.11;
  0.001 0.25 0.88 0.21 0.03 0.25 0.58 0.25;
  0.26 0.58 0.001 0.06 0.9 0.58 0.44 0.15;
  0.12 0.58 0.16 0.08 0.15 0.47 0.33 0.15;
  0.15 0.22 0.3 0.14 0.01 0.99 0.77 0.55;
  0.003 0.25 0.14 0.99 0.005 0.85 0.26 0.003;
  ];
B=[ 0.25 0.55 0.15 0.02;
  0.001 0.25 0.33 0.04;
  0.2 0.3 0.11 0.58;
  0.25 0.14 0.77 0.69;
  0.88 0.59 0.58 0.001;
  0.02 0.3 0.7 0.8;
  0.3 0.9 0.66 0.11;]
C= [ 8 2 4 1
  1 2 3 4
  7 5 2 8
  1 2 3 4
  2 4 3 7
  1 5 6 7
  2 8 4 1]
[rows, columns] = size(B)
newA = A; % Initialize.
for row = 1 : rows
  newA(row, C(row,:)) = B(row, :);
end
newA % Print in command window to verify

MATLAB: Simpler code for aggregating data by sum

A=[4 0.5;4 0.25;1 0.125; 2 0.2;4 0.6;3 0.2; 1 2/3; 2 1; 2 1/16;4 0.5]
Results = [unique(A(:, 1)), accumarray(A(:, 1), A(:, 2))];
Results =
    1.0000    0.7917
    2.0000    1.2625
    3.0000    0.2000
    4.0000    1.8500

Best Answer

Related Solutions

MATLAB: How to replace values in a matrix

MATLAB: Simpler code for aggregating data by sum

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