matlab basic function find

The evolution together a basic computing functions find -matlab

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• Find and index values ​​of nonzero elements

  grammar

• k = find(X)
  • k = find (X) returns a vector, wherein each X comprises an array of non-zero elements linearly indexed .
  • If X is a vector, then find returns a direction vector identical to X
  • If X is a column vector multidimensional array, then find returns the result of the linear index
  • If X does not contain non-zero elements or empty, then find an empty array
• k = find (X, n) k = find (X, n) returns the index of the first n X non-zero elements corresponding to
• k = find (X, n, direction) k = find (X, n, direction), wherein the direction is a 'last', X find the last non-zero elements n
• [Row, col] = find (___) using the input parameters of any preceding syntax Returns an array X non-zero elements of each row and column index

• [Row, col, v] = find (___) returns a vector v, which comprises a non-zero elements of X

  Examples

  Find the matrix elements of zero and non-zero elements

X = [1 0 2; 0 1 1; 0 0 4]
X =

     1     0     2
     0     1     1
     0     0     4

k = find(X)
k =

     1
     5
     7
     8
     9
% 顺序是从上往下从左至右进行排列的
k2 = find(~X)
k2 =

     2
     3
     4
     6

Find the elements that meet certain criteria

X = magic(4)
X =

    16     2     3    13
     5    11    10     8
     9     7     6    12
     4    14    15     1

k = find(X<10,5)
k =

     2
     3
     4
     5
     7

X(k)
ans =

     5
     9
     4
     2
     7

Element is equal to a specific value

• It is equal to the case of particular value using the "==" integer value

x = 1:2:20
x =

     1     3     5     7     9    11    13    15    17    19

k = find(x==13)
k =

     7

• To find the non-integer value, use the tolerance value based data. Otherwise, because the floating point rounding errors, the result sometimes is an empty matrix

y = 0:0.1:1
y =

  Columns 1 through 7

         0    0.1000    0.2000    0.3000    0.4000    0.5000    0.6000

  Columns 8 through 11

    0.7000    0.8000    0.9000    1.0000

k = find(y==0.3)
k =

   Empty matrix: 1-by-0

k = find(abs(y-0.3) < 0.001)
k =

     4

Looking for the last few nonzero project

X = magic(6);
X(1:2:end) = 0 % 索引从左上角往下后往右
X =

     0     0     0     0     0     0
     3    32     7    21    23    25
     0     0     0     0     0     0
     8    28    33    17    10    15
     0     0     0     0     0     0
     4    36    29    13    18    11
% 寻找最后几个非零元素的索引
k = find(X,4,'last')
k =

    30
    32
    34
    36

Looking to meet the multi-constraint

• Find the 4 × 4 matrix in the first three elements of more than 0 to less than 10. Two outputs designated, the row and column index is returned to element

X = [18 3 1 11; 8 10 11 3; 9 14 6 1; 4 3 15 21]
X =

    18     3     1    11
     8    10    11     3
     9    14     6     1
     4     3    15    21

[row,col] = find(X>0 & X<10,3)
row =

     2
     3
     4


col =

     1
     1
     1

And subscript values ​​of nonzero elements

• Seeking 3 × 3 matrix of non-zero elements. Returns the output to the specified three rows superscripts, subscripts and element value column

X = [3 2 0; -5 0 7; 0 0 1]
X =

     3     2     0
    -5     0     7
     0     0     1

[row,col,v] = find(X)
row =

     1
     2
     1
     2
     3


col =

     1
     1
     2
     3
     3


v =

     3
    -5
     2
     7
     1

Input parameters

Output parameters