Thread Subject: help! help!! help!!! me

hello
if
x=linspace(1,100,n);
p=linspace(100,80,n-1);
how can I get A

A=[
x(1) 1 0 0 0 0 0 0...0 0;
x(2) 1 -x(2) -1 0 0 0 0...0 0;
p(1) 0 -p(2) 0 0 0 0 0...0 0;
0 0 x(3) 1 -x(3) -1 0 0...0 0;
0 0 p(2) 0 -p(3) 0 0 0...0 0;
0 0 0 0 x(4) 1 -x(4) -1...0 0;
0 0 0 0 p(3) 0 -p(4) 0...0 0;
......................................
0 0 0 0 0 0...x(i) 1 -x(i) -1...0 0;
0 0 0 0 0 0...p(i-1) 0 -p(i-1) 0 ...0 0;
........................................
0 0 0 0 0 0....x(n-1) 1 -x(n-1) -1;
0 0 0 0 0 0....p(n-2) 0 -p(n-1) 0;
0 0 0 0 0 0.... 0 0 p(n-1) 0;
]

"Jim lei" <redlightlike@mathworks.com> wrote in message
<fkv2u7$t1i$1@fred.mathworks.com>...
> hello
> if
> x=linspace(1,100,n);
> p=linspace(100,80,n-1);
> how can I get A
>
> A=[
> x(1) 1 0 0 0 0 0 0...0 0;
> x(2) 1 -x(2) -1 0 0 0 0...0 0;
> p(1) 0 -p(2) 0 0 0 0 0...0 0;
> 0 0 x(3) 1 -x(3) -1 0 0...0 0;
> 0 0 p(2) 0 -p(3) 0 0 0...0 0;
> 0 0 0 0 x(4) 1 -x(4) -1...0 0;
> 0 0 0 0 p(3) 0 -p(4) 0...0 0;
> ......................................
> 0 0 0 0 0 0...x(i) 1 -x(i) -1...0 0;
> 0 0 0 0 0 0...p(i-1) 0 -p(i) 0 ...0 0;
> ........................................
> 0 0 0 0 0 0....x(n-1) 1 -x(n-1) -1;
> 0 0 0 0 0 0....p(n-2) 0 -p(n-1) 0;
> 0 0 0 0 0 0.... 0 0 p(n-1) 0;
> ]

"Jim lei" <redlightlike@mathworks.com> wrote in message
<fkv3c9$61e$1@fred.mathworks.com>...
> "Jim lei" <redlightlike@mathworks.com> wrote in message
> <fkv2u7$t1i$1@fred.mathworks.com>...
> > hello
> > if
> > x=linspace(1,100,n);
> > p=linspace(100,80,n-1);
> > how can I get A
> >
> > A=[
> > x(1) 1 0 0 0 0 0 0...0 0;
> > x(2) 1 -x(2) -1 0 0 0 0...0 0;
> > p(1) 0 -p(2) 0 0 0 0 0...0 0;
> > 0 0 x(3) 1 -x(3) -1 0 0...0 0;
> > 0 0 p(2) 0 -p(3) 0 0 0...0 0;
> > 0 0 0 0 x(4) 1 -x(4) -1...0 0;
> > 0 0 0 0 p(3) 0 -p(4) 0...0 0;
> > ......................................
> > 0 0 0 0 0 0...x(i) 1 -x(i) -1...0 0;
> > 0 0 0 0 0 0...p(i-1) 0 -p(i) 0 ...0 0;
> > ........................................
> > 0 0 0 0 0 0....x(n-1) 1 -x(n-1) -1;
> > 0 0 0 0 0 0....p(n-2) 0 -p(n-1) 0;
> > 0 0 0 0 0 0.... 0 0 p(n-1) 0;
> > ]
>
Divide your matrix into sub-matrices, and then combine them.

%%
Ax1 = zeros(n-2,n-1);
Ax2 = zeros(n-2,n-1);
diagpos = sub2ind([n-2 n-1],1:n-2,1:n-2);

Ax1(diagpos) = x(2:end-1);
Ax1(diagpos+n-2) = -x(2:end-1);

Ax2(diagpos) = 1;
Ax2(diagpos+n-2) = -1;

% Ax = reshape(cat(1,Ax1,Ax2),[size(Ax1,1)
size(Ax1,2)+size(Ax2,2)])
Ax = zeros(n-2,2*n-2);
Ax(:,1:2:end) = Ax1;
Ax(:,2:2:end) = Ax2;

%%
Ap1 = zeros(n-2,n-1);
Ap1(diagpos) = p(1:n-2);
Ap1(diagpos+n-2) = -p(2:n-1);

Ap = zeros(n-2,2*n-2);
Ap(:,1:2:end-1) = Ap1;
%%
A = zeros(2*n-2,2*n-2);

A(2:2:end-2,:) = Ax;
A(3:2:end,:) = Ap;
A(1,[1 2]) = [x(1) 1];
A(end,end-1) = p(end);


Anh Huy Phan
RIKEN - BSI

In article <fkv2u7$t1i$1@fred.mathworks.com>,
Jim lei <redlightlike@mathworks.com> wrote:

>if
>x=linspace(1,100,n);
>p=linspace(100,80,n-1);
>how can I get A

>A=[
>x(1) 1 0 0 0 0 0 0...0 0;
>x(2) 1 -x(2) -1 0 0 0 0...0 0;
>p(1) 0 -p(2) 0 0 0 0 0...0 0;
>0 0 x(3) 1 -x(3) -1 0 0...0 0;
>0 0 p(2) 0 -p(3) 0 0 0...0 0;
>0 0 0 0 x(4) 1 -x(4) -1...0 0;
>0 0 0 0 p(3) 0 -p(4) 0...0 0;
>......................................
>0 0 0 0 0 0...x(i) 1 -x(i) -1...0 0;
>0 0 0 0 0 0...p(i-1) 0 -p(i-1) 0 ...0 0;
>........................................
>0 0 0 0 0 0....x(n-1) 1 -x(n-1) -1;
>0 0 0 0 0 0....p(n-2) 0 -p(n-1) 0;
>0 0 0 0 0 0.... 0 0 p(n-1) 0;
>]

See the functions diag() and blkdiag().

Also, please use a more descriptive topic name.

Another note: when you post requesting urgent help without describing
your timeframe, then after a couple of hours, people are likely not
to reply, figuring that your deadline has likely already passed. Or
sometimes, perhaps even within the first few hours, they may choose
not to respond, with thoughts about it being irresponsible of you
to have left the task to the last minute. There is a saying,
"Your bad planning does not my emergency make."
--
   So you found your solution
   What will be your last contribution?
   -- Supertramp (Fool's Overture)