å½ä»¤ æ±æ ·æ¬æ¹å·®
å½æ° var
æ ¼å¼ D=var(X) %var(X)= ,è¥X为åéï¼åè¿ååéçæ ·æ¬æ¹å·®ã
D=var(A) %A为ç©éµï¼åD为Aç
ååéçæ ·æ¬æ¹å·®ææçè¡åéã
D=var(X, 1) %è¿ååéï¼ç©éµï¼Xçç®åæ¹å·®ï¼å³ç½®åå å为 çæ¹å·®ï¼
D=var(X, w) %è¿ååéï¼ç©éµï¼Xç以w为æéçæ¹å·®
è¯ççè¿ä¸ª
-------------------------------------------------------------------------------
åå¼
ä¾å¦ï¼
>> X=1:10
X =
1 2 3 4 5 6 7 8 9 10
>> mean(X)
ans =
5.5000
>> var(X)
ans =
9.1667
-------------------------------------------------------------------
å¹³æ¹
function cholesky(A,b,n)
s=0;
p=0;
for j=1:n
s=0;
p=0;
if j==1
l(j,j)=A(j,j)^(1/2);
for q=(j+1):n
l(q,j)=A(q,j)/l(j,j);
end
else
for k=1:(j-1)
s=s+l(j,k).^2;
end
l(j,j)=(A(j,j)-s)^(1/2);
for q=(j+1):n
for k=1:(j-1)
p=p+l(q,k)*l(j,k);
end
l(q,j)=(A(q,j)-p)/l(j,j);
end
end
end
for i=1:n
s=0;
if i==1
y(i)=b(i)/l(i,i);
else
for k=1:(i-1)
s=s+l(i,k)*y(k);
end
y(i)=(b(i)-s)/l(i,i);
end
end
l=l';
for i=n:-1:1
s=0;
if i==n
x(i)=y(i)/l(i,i);
else
for k=(i+1):n
s=s+l(i,k)*x(k);
end
x(i)=(y(i)-s)/l(i,i);
end
end
y
x
-----------------------------------------------------------------------------
æ±éæºæ°çå
èç¹å¡ç½æ¨¡æ
å°±æ¯éæºæ°ç¸å
³çä¸è¥¿ï¼ä½ åªè¦ç¥ééæºæ°æ¯æä¹å¾å°ãå
¶å®çäºå°±è¦å¥½åäºã
rand(m,n)产çm*nååéæºæ°ã
ex:
ç¨æ¦çæ¹æ³æ±pi
N=100000;
x=rand(N,1);
y=rand(N,1);
count=0;
for i=1:N
if (x(i)^2+y(i)^2<=1)
count=count+1;
end
end
PI=4*count/N