在已知协方差存在下的最小二乘溶液
X = LSCOV(A,B)
X= lscov(A,B,w)
X= lscov(A,B,V)
X= lscov(A,B,V,alg)
[x,stdx] = lscov(...)
[x,stdx,mse] = lscov(...)
[x,stdx,mse,s] = lscov(...)
X = LSCOV(A,B)
将普通的最小二乘解返回到线性系统的方程式一种*x = B
,即,X
is the n-by-1 vector that minimizes the sum of squared errors(b - a * x)'*(b - a * x)
,在哪里一种
是m-by-n,和B.
is m-by-1.B.
也可以是m-by-k矩阵,和LSCOV.
为每列返回一个解决方案B.
。什么时候等级(a)
LSCOV.
sets the maximum possible number of elements ofX
to zero to obtain a "basic solution".
X= lscov(A,B,w)
,在哪里W.
is a vector length m of real positive weights, returns the weighted least squares solution to the linear system一种*x = B
, 那是,X
minimizes(B - A*x)'*diag(w)*(B - A*x)
。W.
typically contains either counts or inverse variances.
X= lscov(A,B,V)
,在哪里V.
是一个m-by-m真正的对称正定矩阵,将广义最小二乘解返回线性系统一种*x = B
W.ith covariance matrix proportional toV.
, 那是,X
minimizes(b - a * x)'* inv(v)*(b - a * x)
。
More generally,V.
can be positive semidefinite, andLSCOV.
回报X
that minimizesE.'*e
,约束一种*x + T*e = B
,在哪里the minimization is overX
andE.
那andt * t'= v
。什么时候V.
是Semidefinite,这个问题只有一个解决方案B.
和......一致一种
andV.
(那是,B.
处于列空间[在]
), 除此以外LSCOV.
返回错误。
默认,LSCOV.
计算Cholesky分解V.
并且,实际上,反转该因素将问题转变为普通的最小二乘。但是,如果LSCOV.
确定V.
is semidefinite, it uses an orthogonal decomposition algorithm that avoids invertingV.
。
X= lscov(A,B,V,alg)
specifies the algorithm used to computeX
什么时候V.
是一个矩阵。alg
可以具有以下值:
'chol'
uses the Cholesky decomposition ofV.
。
'orth'
使用正交分解,并且更合适的时间V.
是不良状态或单数,但是计算得更昂贵。
[x,stdx] = lscov(...)
返回估计的标准错误X
。什么时候一种
排名缺乏,STDX.
contains zeros in the elements corresponding to the necessarily zero elements ofX
。
[x,stdx,mse] = lscov(...)
返回平均方形错误。如果B.
假设具有协方差矩阵σ2V.
(或(σ2)×诊断接头
(1. /W.
)), 然后mse
is an estimate of σ2。
[x,stdx,mse,s] = lscov(...)
返回估计的协方差矩阵X
。什么时候一种
排名缺乏,S.
contains zeros in the rows and columns corresponding to the necessarily zero elements ofX
。LSCOV.
cannot returnS.
if it is called with multiple right-hand sides, that is, ifsize(B,2) > 1
。
这些数量的标准公式,何时一种
andV.
是全级别,是
x = inv(a'* inv(v)* a)* a'* inv(v)* b
mse = b'*(inv(v) - inv(v)* a * inv(a'* inv(v)* a)* a'* inv(v))* b./()
s = inv(a'* inv(v)* a)* mse
stdx = sqrt(diag(s))
However,LSCOV.
使用更快更稳定的方法,并且适用于等级缺乏案例。
LSCOV.
假设协方差矩阵B.
只知道达到比例因素。mse
is an estimate of that unknown scale factor, andLSCOV.
scales the outputsS.
andSTDX.
appropriately. However, ifV.
is known to be exactly the covariance matrix ofB.
,然后不需要缩放。要在这种情况下获得适当的估计,您应该重新归类S.
andSTDX.
通过1 / MSE.
andSQRT(1 / MSE)
, 分别。
The MATLAB®backslash operator (\) enables you to perform linear regression by computing ordinary least-squares (OLS) estimates of the regression coefficients. You can also useLSCOV.
计算相同的OLS估计值。通过使用LSCOV.
,您还可以计算这些系数的标准错误的估计,以及回归错误项的标准偏差的估计值:
X1 = [.2 .5 .6 .8 1.0 1.1]';X2 = [.1 .3 .4 .9 1.1 1.4]';x = [(尺寸(x1))x1 x2];Y = [.17 .26 .28 .23 .27 .34]';a = x \ y a = 0.1203 0.1203 0.3284 -0.1312 [SE_B,MSE] = LSCOV(X,Y)B = 0.1203 0.3284 -0.1312 SE_B = 0.0643 0.2267 0.1488 MSE = 0.0015
UseLSCOV.
to compute a weighted least-squares (WLS) fit by providing a vector of relative observation weights. For example, you might want to downweight the influence of an unreliable observation on the fit:
w = [1 1 1 1 1 .1]';[BW,SEW_B,MSEW] = LSCOV(X,Y,W)BW = 0.1046 0.4614 -0.2621 SEF_B = 0.0309 0.1152 0.0814 MSEW = 3.4741E-004
UseLSCOV.
to compute a general least-squares (GLS) fit by providing an observation covariance matrix. For example, your data may not be independent:
v = .2 *那些(长度(x1))+ .8 * diag(inal(尺寸(x1)));[BG,SEW_B,MSEG] = LSCOV(X,Y,V)BG = 0.1203 0.3284 -0.1312 SEF_B = 0.0672 0.2267 0.1488 MSEG = 0.0019
计算OLS,WLS或GLS的系数协方差矩阵的估计。系数标准误差等于该协方差矩阵对角线上的值的平方根:
[b,se_b,mse,s] = lscov(x,y);S S = 0.0041 -0.0130 0.0075 -0.0130 0.0514 -0.0328 0.0075 -0.0328 0.0221 0.0221 0.0221 0.02210.0221 0.06430.0643 0.0643 0.2267 0.2267 0.2267 0.2267 0.1488 0.22267 0.2267 0.0643 0.2267 0.22267 0.2267 0.06430.2267
矢量X
最小化数量(a * x-b)'* inv(v)*(a * x-b)
。The classical linear algebra solution to this problem is
x = inv(a'* inv(v)* a)* a'* inv(v)* b
但是LSCOV.
函数来计算QR分解一种
and then modifies问:
通过V.
。
[1]斯特朗,G.,应用数学介绍那W.E.llesley-Cambridge, 1986, p. 398.