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Showing posts from January, 2010

Customised search in Linux using find

Below is a code to customise search in Linux using find. find would recurse through all the directories. I needed to omit some directories which I knew didn't have the file I was looking for but instead have games. So recursing through them would cause enormous processor overhead and time loss. So I wrote a code in shell script to omit specific directories..

cd /
for aa in `ls`
do

if [ "$aa" != "resident_evil" ] ; then
if [ "$aa" != "usr1" ] ; then
if [ "$aa" != "usr2" ] ; then
if [ "$aa" != "usr3" ] ; then
if [ "$aa" != "unreal" ] ; then
if [ "$aa" != "quake3" ] ; then
echo -e " Current search path: "
cd $aa
pwd
find . -name "*.a"
fi
fi
fi
fi
fi
fi


cd /

done

TT OPE for bc ghosts and massless fermions

While calculating T(z) T(w) OPE for bc ghosts and massless fermions I came across a weird result.

I could get the central charge correct and also the T(w)/(z-w)^2 term correct but the other terms which remain does not add up to T(w) as expected.

In massless fermion case:

T = :ψ ψ:

T(z) T(w) = 1/4/(z-w)^4 + T(w)/(z-w)^2 + ( 1/2 ψ ∂2 ψ + ∂ ψ ∂ ψ )/(z-w)

But,
∂ T = ψ ∂2 ψ + ∂ ψ ∂ ψ

So, I cannot account for the 1/2 factor in front of ψ ∂2 ψ .

In bc ghost case :

T = : 2 c b + c b :

T(z) T(w) = 1/4/(z-w)^4 + T(w)/(z-w)^2 + ( 4 ∂2c b + 3 ∂c ∂b - c ∂2b)/(z-w)

But,
∂T = 2 ∂2c b + 3 ∂c ∂b + c ∂2b

This means I have some terms like

T(z) T(w) = 1/4/(z-w)^4 + T(w)/(z-w)^2 + ( 4 ∂2c b + 3 ∂c ∂b - c ∂2b)/(z-w)
= 1/4/(z-w)^4 + T(w)/(z-w)^2 + [∂ T + 2( ∂2c b - c ∂2b)]/(z-w)
= 1/4/(z-w)^4 + T(w)/(z-w)^2 + ∂ [ T + 2 ( ∂c b - c ∂b) ]/(z-w)

I have no idea why the term ( ∂c b - c ∂b) should be zero.

So the problem is:
1. Whether it is correct to directly differentiate expression for T(z) to get the ∂T(z…

Convert HTML to PDF

In linux it is very easy. Install CUPS-PDF and print to PDF. I explained it in another post previously. But sadly, if I follow this printing procedure the hyperlinks are not preserved in the resulting pdf file. So the alternatively we can use htmldoc to convert HTML to PDF. The command is -

$ htmldoc lec.html --webpage -t pdf14 -f lec.pdf

--webpage : turns on the webpage mode.
-t : sets the output pdf type.
-f : output filename.

That's it. If you do not have htmldoc pre-install then install it with sudp apt-get install htmldoc in Ubuntu.

Petrov classification

gr-qc/0512087v1
I read Petrov classification of 4 tensors and Serge classification of 2 tensors. Will it help my project on membrane paradigm? I don't know. But it is good to learn how a 4 tensor can be decomposed. I want to know more of this.