diagonal matrix--diag

how to create a diagonal matrix?

diag() func.

how to get diagonal elements from a matrix?

diag() func.

[syntax][descr]

(1) M=diag(Vector V,int k=0)

will return a |V|*|V| diagonal matrix

|V| is length of V

When k=0, M is |V|*|V| size, M[i,i]=v[i] , M[i,j]=0 , for 1<=i , j <=|V| i!=j , where i and j is positive integer.

i.e. value of elements in M which its index belongs diagonal is equal to value of elements in Vector V, otherwise is equal to 0.

translation:對角線索引的值為V的元素的值，非對角線索引的值為0

When k>0, M is |V+k|*|V+k| size, M[i+k,i+k]=v[i] ,M[i,j]=0 for 1<=i , j <=|V| i!=j , where i , j and k is positive integer.

[extra tips] You can think about M=diag(V), then add a row and column at left and button which all element are equal to 0.

translation:你可以想M=diag(V)，然後把所有為0的元素加到最左行(第一行)和最下列(最後一列)

When k<0, M is |V+k|*|V+k| size, M[i,i]=v[i] ,M[i,j]=0 for 1<=i , j <=|V| i!=j , where i and j is positive integer. k is negative integer.

[extra tips] You can think about M=diag(V), then add a row and column at right and up which all element are equal to 0.

translation:你可以想M=diag(V)，然後把所有為0的元素加到最右行(最後一行)和最上列(第一列)

(2) diag(matrix A,int k=0)

When k=0, it will return all diagonal elements of A.

When k>0, it will return all elements of M[i,k+i] for all i in 1<=i<=k

When k<0, it will return all elements of M[i+k,i] for all i in 1<=i<=k

more deatils on

official website:

Programming-MatLab