## Sunday, January 27, 2013

### MCMC

Doing MCMC is fun! Thanks to KnuthClass
aa
% probability step
if x(n) < 0
px = 3/5;
else
px = 2/5;
end

% Metropolis Hastings MCMC

p = min([1, p(y)/p(x(n))]);
r = rand;

n = n+1;
if r < p
x(n) = y;
else
x(n) = x(n-1);
end

%%

% do this 100 times

x(1) = 1;   % start in the low prob region
px(1) = 2/5;

for n = 1:10000

% take a step
y = (-1)*x(n);

% probability step
if y < 0
py = 3/5;
else
py = 2/5;
end

% Metropolis Hastings MCMC
p = min([1, py/px(n)]);
r = rand;

%n = n+1;
if r < p
x(n+1) = y;
px(n+1) = py;
else
x(n+1) = x(n);
px(n+1) = px(n);
end

x(n)

end

%%
clear

% Gaussian probability density with zero mean and unit variance
prob = @(z)((sqrt(2*pi))^(-1)*exp(-z^2/2));

x(1) = 5*(2*rand-1);
px(1) = prob(x);

for n = 1:100000
step = 0.01*randn;
y = x(n)+step;

py = prob(y);

p = min([1,py/px(n)]);
r = rand;

if r < p
x(n+1) = y;
px(n+1) = py;
else
x(n+1) = x(n);
px(n+1) = px(n);
end
end

aa

## Wednesday, January 23, 2013

### Blogger Trick hide the post/widget in main page

Well, I wanted to replace some of the widgets to invisible mode in nabinkm.com. Actually, wanted for long time...
<b:if cond='data:blog.pageType != "index"'>

the widget goes here...

</b:if>

Another trick is: replacing
]]></b:skin>

by

]]></b:skin>
<b:if cond="data:blog.url == data:blog.homepageUrl">
<style type="text/css">
.post,   #blog-pager {display:none;}
</style>
</b:if>
<b:if cond="data:blog.url == data:blog.homepageUrl">
<style type="text/css">
body#layout .sidebar {display:inline;margin-top:200px;}
</style>
</b:if>
-->