MATLAB: How to create a loop on matrix

vincent

Assuming you have a 4×10 matrix. How do you create a loop from the 2nd column of the matrix to the 10th column.

Best Answer

for example suppose we want to multiply each column by its coulmn number:

A =[
    92    99     1     8    15    67    74    51    58    40
    98    80     7    14    16    73    55    57    64    41
     4    81    88    20    22    54    56    63    70    47
    85    87    19    21     3    60    62    69    71    28
    ]
for it=2:10
    A(:,it) = A(:,it)*it;
end
A

A =

92 198 3 32 75 402 518 408 522 400

98 160 21 56 80 438 385 456 576 410

4 162 264 80 110 324 392 504 630 470

85 174 57 84 15 360 434 552 639 280

Related Solutions

MATLAB: I want to transfer data from a for loop into a vector, i need to use rows of a matrix, every 3rd number(not every 3rd entry) in first column( 2 to 5 repeated numbers for each, tho random). Prob is output length unknown so difficult to prelocate

We can avoid the loop altogether by using the very efficient bsxfun instead:

x = [1,4,7,10,13,16,19,22,25,28,31,34,37,40,43,46,49,52,55,58,61,64,67,70,73,76,79,82,85,88,91,94,97,100,103,106,109,112,115,118,121,124,127,130,133,136,139,142,145,148,151,154,157,160,163,166,169,172,175,178,181,184,187,190,193,196,199,202,205,208,211,214,217,220,223,226,229,232,235,238,241,244,247,250,253,256,259,262,265,268,271,274,277,280,283,286,289,292,295,298,301,304,307,310,313,316,319,322,325,328,331,334,337,340,343,346,349,352,355,358,361,364,367,370,373,376,379,382,385,388,391,394,397,400,403,406,409,412,415,418,421,424,427,430,433,436,439,442,445,448,451,454,457,460,463,466,469,472,475,478,481,484,487,490,493,496,499,502,505,508,511,514,517,520,523,526,529,532,535,538,541,544,547,550,553,556,559,562,565,568,571,574,577,580,583,586,589,592,595,598,601,604,607,610,613,616,619,622,625,628,631,634,637,640,643,646,649,652,655,658,661,664,667,670,673,676,679,682,685,688,691,694,697,700,703,706,709,712,715,718,721,724,727,730,733,736,739,742,745,748];
B(:,2) = 1:6;
B(:,1) = [40,0,106,0,0,487]
idx = any(bsxfun(@eq,B(:,1),x),2);
out = B(idx,:)

which displays this in the command window:

>> Untitled
B =
    40     1
     0     2
   106     3
     0     4
     0     5
   487     6
out =
    40     1
   106     3
   487     6

This is a kind of code vectorization, which is important to learn if you want to use MATLAB efficiently.

MATLAB: How do you set the first column of a 4×4 matrix = a vector

X = [380 250 220 200]
C=[1257 679 220 203
    1567 155 234 432
    2345 445 238 556];
C(1,:)=X; % set the first row of C equal to vector X

size of C = 3*4 , and size of X = 1*4. you can set the first row of C equal to X. if not, I assume it was:

X = [380; 250; 220; 200]
C=[1257 679 220
    203 1567 155
    234 432 2345
    445 238 556];
C(:,1)=X; % set the first column of C equal to vector X

Best Answer

Related Solutions

MATLAB: I want to transfer data from a for loop into a vector, i need to use rows of a matrix, every 3rd number(not every 3rd entry) in first column( 2 to 5 repeated numbers for each, tho random). Prob is output length unknown so difficult to prelocate

MATLAB: How do you set the first column of a 4×4 matrix = a vector

Related Question