matlab矩阵元素位置怎么返回?

FIND Find indices of nonzero elements.
I = FIND(X) returns the indices of the vector X that are
non-zero. For example, I = FIND(A>100), returns the indices
of A where A is greater than 100. See RELOP.

[I,J] = FIND(X) returns the row and column indices of
the nonzero entries in the matrix X. This is often used
with sparse matrices.

[I,J,V] = FIND(X) also returns a vector containing the
nonzero entries in X. Note that find(X) and find(X~=0)
will produce the same I and J, but the latter will produce
a V with all 1's.

See also SPARSE, IND2SUB.