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转载地址:https://en.wikipedia.org/wiki/System_of_linear_equations#Solving_a_linear_system
由于很多地方需要求解 齐次,非齐次线性方程,把线代,高数书毕业了都扔了,汗,简单总结一下。
实际中都是用Eigen 库,调用API解线性方程组,得注意每个函数的适用条件。
where A is an m×n matrix, x is a column vector with n entries, and b is a column vector with m entries.
其中:A的行向量之间线性无关,这样每一行带来的才是关于参数新的约束信息。
In general, the behavior of a linear system is determined by the relationship between the number of equations and the number of unknowns:
- Usually, a system with fewer equations than unknowns has infinitely many solutions, but it may have no solution. Such a system is known as an underdetermined system.
- Usually, a system with the same number of equations and unknowns has a single unique solution.
- Usually, a system with more equations than unknowns has no solution. Such a system is also known as an overdetermined system.(在实际中,我们往往用线性最小二乘的方法求X,使得|| b-AX || 最小)
的解 只有两种:
零解和非零解(无数多个)。
A假设为: m*n , r(A)=r
当 r=n, 只有零解;
当 r<n , n-r个基础解系,即有非零解;
的解 : SVD
Solving homogeneous linear equations[edit]
A set of homogeneous linear equations can be written as Ax = 0 for a matrix A and vector x. A typical situation is that A is known and a non-zero x is to be determined which satisfies the equation. Such an x belongs to A's null space and is sometimes called a (right) null vector of A.
解: The vector x can be characterized as a right-singular vector corresponding to a singular value of A that is zero.
This observation means that if A is a square matrix and has no vanishing singular value, the equation has no non-zero x as a solution. It also means that if there are several vanishing(零值)singular values, any linear combination of the corresponding right-singular vectors is a valid solution. Analogously to the definition of a (right) null vector, a non-zero x satisfying x∗A = 0, with x∗ denoting the conjugate transpose of x, is called a left null vector of A.
AX=b的解
If the equation system is expressed in the matrix form, the entire solution set can also be expressed in matrix form. If the matrix A is square (has m rows and n=m columns) and has full rank (all m rows are independent), then the system has a unique solution given by
where is the inverse of A.
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