matlab中svd函数用法总结
2017-05-30 14:11
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1、帮助文档
svd
Singular value decomposition
Syntax
s = svd(X)[U,S,V] = svd(X)
[U,S,V] = svd(X,0)
[U,S,V] = svd(X,'econ')
Description
The svd command computes the matrix singularvalue decomposition.s = svd(X) returns a vectorof singular values.
[U,S,V] = svd(X) producesa diagonal matrix S of the same dimension as X,with nonnegative diagonal elements in decreasing order, and unitarymatrices U and V so
that X= U*S*V'.
[U,S,V] = svd(X,0) producesthe "economy size" decomposition. If X ism-by-n with m > n, then svd computes onlythe first ncolumns of U and S isn-by-n.
[U,S,V] = svd(X,'econ') also produces the"economy size" decomposition. If X ism-by-n with m >= n, it is equivalent tosvd(X,0).For m < n, only the first m columns of V arecomputed and S is m-by-m.
Examples
For the matrixX = 1 2 3 4 5 6 7 8
the statement
[U,S,V] = svd(X)
produces
U = -0.1525 -0.8226 -0.3945 -0.3800 -0.3499 -0.4214 0.2428 0.8007 -0.5474 -0.0201 0.6979 -0.4614 -0.7448 0.3812 -0.5462 0.0407 S = 14.2691 0 0 0.6268 0 0 0 0 V = -0.6414 0.7672 -0.7672 -0.6414
The economy size decomposition generated by
[U,S,V] = svd(X,0)
produces
U = -0.1525 -0.8226 -0.3499 -0.4214 -0.5474 -0.0201 -0.7448 0.3812 S = 14.2691 0 0 0.6268 V = -0.6414 0.7672 -0.7672 -0.6414
Diagnostics
If the limit of 75 QR step iterations is exhausted while seekinga singular value, this message appears:Solution will not converge.
2、使用误区
>> S=svd(A)??? Undefined function or method 'svd' for input arguments of type 'uint8'.
出错原因,A的数据类型为uint8
解决办法S=svd(double(A))
>> S=SVD(double(A))
??? Undefined function or method 'SVD' for input arguments of type 'double'.
出错原因,SVD在R2011a中不能被调用,区分大小写
解决办法S=svd(double(A))
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