# Large substitution from symbolic matrix to numerical values while keeping 4 unknowns into the new matrix

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petit on 25 Apr 2021
Commented: petit on 25 Apr 2021
I have to solve the equality between 2 matrixes 12x12 containing a lot of symbolic variables and with which I perform inversion of matrix. There are only one unknown called `SIGAM_O, and FISH_O_SYM(1,1), FISH_O_SYM(1,2) and FISH_O_SYM(2,2) (FISH_O_SYM(2,1) = FISH_O_SYM(1,2)`.
My system is solved fastly when I take for example 2 matrices 2x2, the inversion is pretty direct.
Now, with the case of 2 matrixes 12x12, I need before actually to inverse a 31x31 matrix of symbolic variables (I marginalize after), since inversion takes a lot of time.
I would like to benefit from my GPU NVIDIA card to achieve this inversion faster but the GPU optimization is not supported currently for Symbolic arrays.
Below the script where you will find the line of inversion :
COV_ALL = inv(FISH_SYM)
and the entire code :
clear;
clc;
format long;
% 2 Fisher Matrixes symbolic : FISH_GCsp_SYM, : 1 cosmo params + 1 bias spectro put for common
% FISH_XC_SYM : 1 cosmo params + 2 bias photo correlated
% GCsp Fisher : 7 param cosmo and 5 bias spectro which will be summed
FISH_GCsp_SYM = sym('sp_', [17,17], 'positive');
% Force symmetry for GCsp
FISH_GCsp_SYM = tril(FISH_GCsp_SYM.') + triu(FISH_GCsp_SYM,1)
% GCph Fisher : 7 param cosmo + 3 I.A + 11 bias photo correlated
FISH_XC_SYM = sym('xc_', [21,21], 'positive');
% Force symmetry for GCph
FISH_XC_SYM = tril(FISH_XC_SYM.') + triu(FISH_XC_SYM,1)
% Brutal Common Bias : sum of 7 cosmo param ans 5 bias spectro : FISH_ALL1 = first left matrix
FISH_ALL1 = sym('xc_', [12,12], 'positive');
% Sum cosmo
FISH_ALL1(1:7,1:7) = FISH_GCsp_SYM(1:7,1:7) + FISH_XC_SYM(1:7,1:7);
% Brutal sum of bias
FISH_ALL1(7:12,7:12) = FISH_GCsp_SYM(7:12,7:12) + FISH_XC_SYM(15:20,15:20);
% Adding new observable "O" terms
FISH_O_SYM = sym('o_', [2,2], 'positive');
% Definition of sigma_o
SIGMA_O = sym('sigma_o', 'positive');
FISH_O_SYM = 1/(SIGMA_O*SIGMA_O) * FISH_O_SYM
% Force symmetry
FISH_O_SYM = (tril(FISH_O_SYM.') + triu(FISH_O_SYM,1))
FISH_O_SYM
%FISH_SYM = sym('xc_', [31,31], 'positive');
%FISH_BIG_GCsp = sym('sp_', [31,31], 'positive');
%FISH_BIG_XC = sym('xc_', [31,31], 'positive');
FISH_SYM = zeros(31,31,'sym');
FISH_BIG_GCsp = zeros(31,31,'sym');
FISH_BIG_XC = zeros(31,31,'sym');
% Block bias spectro + pshot and correlations;
FISH_BIG_GCsp(1:7,1:7) = FISH_GCsp_SYM(1:7,1:7);
FISH_BIG_GCsp(7:17,7:17) = FISH_GCsp_SYM(7:17,7:17);
FISH_BIG_GCsp(1:7,7:17) = FISH_GCsp_SYM(1:7,7:17);
FISH_BIG_GCsp(7:17,1:7) = FISH_GCsp_SYM(7:17,1:7);
% Block bias photo and correlations;
FISH_BIG_XC(1:7,1:7) = FISH_XC_SYM(1:7,1:7);
FISH_BIG_XC(21:31,21:31) = FISH_XC_SYM(11:21,11:21);
FISH_BIG_XC(1:7,21:31) = FISH_XC_SYM(1:7,11:21);
FISH_BIG_XC(21:31,1:7) = FISH_XC_SYM(11:21,1:7);
% Block I.A and correlations;
FISH_BIG_XC(18:20,18:20) = FISH_XC_SYM(8:10,8:10);
FISH_BIG_XC(1:7,18:20) = FISH_XC_SYM(1:7,8:10);
FISH_BIG_XC(18:20,1:7) = FISH_XC_SYM(8:10,1:7);
% Final summation
FISH_SYM = FISH_BIG_GCsp + FISH_BIG_XC;
FISH_SYM(6,6) = FISH_SYM(6,6) + FISH_O_SYM(1,1);
FISH_SYM(6,26) = FISH_SYM(6,26) + FISH_O_SYM(2,2);
FISH_SYM(26,6) = FISH_SYM(26,6) + FISH_O_SYM(1,2);
FISH_SYM(26,26) = FISH_SYM(26,26) + FISH_O_SYM(2,1);
% Force symmetry
FISH_SYM = (tril(FISH_SYM.') + triu(FISH_SYM,1))
% Marginalize FISH_SYM2 in order to get back a 2x2 matrix
% Invert to marginalyze : take a long long time
COV_ALL = inv(FISH_SYM);
% Marginalize
COV_ALL([13:31],:) = [];
COV_ALL(:,[13:31]) = [];
FISH_ALL2 = inv(COV_ALL);
FISH_ALL1
FISH_ALL2
% Matricial equation to solve
eqn = FISH_ALL1 == FISH_ALL2;
% Solving : sigma_o unknown
[solx, parameters, conditions] = solve(eqn, SIGMA_O, 'ReturnConditions', true);
solx
Actually, this inversion of 31x31 size takes a long long time (I had to stop it).
So, now, the strategy is to replace almost all the symolic unknowns by numerical values : I want just to keep 4 unknown (`SIGAM_O, and FISH_O_SYM(1,1), FISH_O_SYM(1,2) and FISH_O_SYM(2,2) (FISH_O_SYM(2,1) = FISH_O_SYM(1,2)`)
So, I would like to know how to do a large substitution of arrays `FISH_XC_SYM` and `FISH_GCsp_SYM` by numerical values of the equivalent of these 2 matrixes.
I could do for example :
But how to assign quickly to the both arrays `FISH_GCsp_SYM` and `FISH_XC_SYM` the numerical values of arrays `FISH_GCsp_NUM` and `FISH_XC_NUM`, al of this while keeping the 4 unknown above ?
Best regards
##### 2 CommentsShowHide 1 older comment
petit on 25 Apr 2021
the strategy that I would like to apply is slightly different from the previous question. Indeed, here it is about a global substitution on symbolic variables by numerical values. So I thought this would deserve a new question.
Sorry if it is diturbing for you but it seems to be appropriate for me.
Best regards