change_of_basis

Change of basis is a useful transformation in a lot of aspect. This page shows how to use command CoB to apply change of basis on a program.

Here is the usage for CoB:

CoB(Program program, String systemName, String varName, String function)The meaning for each parameters are:

- program: the program you are processing.
- systemName: the name for the system you want to solve.
- varName: the name for the variable you want to apply change of basis on.
- function: change of basis function.

The following example does a matrix multiplication, C = A*B.

affine matrix_product {P, Q, R|P>0 && Q>0 && R>0} given float A {i,k| 0<=i<P && 0<=k<Q}; float B {k,j| 0<=k<Q && 0<=j<R}; returns float C {i,j,k| 0<=i<P && 0<=j<R && k==Q}; using // Using an accumulator locally float temp_C {i,j,k|0<=i<P && 0<=j<R && 0<=k<=Q}; through temp_C = case {i,j,k|k-1>= 0} : ((i,j,k->i,j,k-1)@temp_C + ((i,j,k->i,k-1)@A * (i,j,k->k-1,j)@B)); {i,j,k|k== 0} : (i,j,k->)@0; esac; C = (i,j,k->i,j,k)@temp_C; .Now we are going to apply change of basis on variable “temp_C” using function (i,j,k→i,j,k+1). We can apply the transformation with the following code:

prog = ReadAlphabets("matrix_product.ab"); system = "matrix_product"; CoB(prog, system, "temp_C", "(i,j,k->i,j,k+1)");

The result for this transformation is shown below:

affine matrix_product {P, Q, R|P>0 && Q>0 && R>0} given float A {i,k| 0<=i<P && 0<=k<Q}; float B {k,j| 0<=k<Q && 0<=j<R}; returns float C {i,j,k| 0<=i<P && 0<=j<R && k==Q}; using // Using an accumulator locally float temp_C {i,j,k|0<=i<P && 0<=j<R && 1<=k<=Q+1}; through temp_C = (i,j,k->i,j,k-1)@case {i,j,k|k-1>= 0} : ((i,j,k->i,j,k-1)@(i,j,k->i,j,k+1)@temp_C + ((i,j,k->i,k-1)@A * (i,j,k->k-1,j)@B)); {i,j,k|k== 0} : (i,j,k->)@0; esac; C = (i,j,k->i,j,k)@(i,j,k->i,j,k+1)@temp_C; .We applied the change of basis function (i,j,k→i,j,k+1) on variable “temp_C”, which means we shifted the domain of “temp_C” along k direction by one unit. We can see that the domain for “temp_C” is changed from:

float temp_C {i,j,k|0<=i<P && 0<=j<R && 0<=k<=Q};to

float temp_C {i,j,k|0<=i<P && 0<=j<R && 1<=k<=Q+1};And all the access functions for temp_C is composed with function (i,j,k→i,j,k+1). For example, the access function in the computation of C is changed from

C = (i,j,k->i,j,k)@temp_C;to

C = (i,j,k->i,j,k)@(i,j,k->i,j,k+1)@temp_C;

change_of_basis.txt · Last modified: 2017/04/19 14:15 (external edit)