MATLAB: How to use imported data in matlab equations

4 equations and 4 unknownsMATLAB

Hi to everyone:
i have four equations and four unknowns which is given below:
s*x+4y-3z+12m=100
2x+3*s*y+4z+200m=200
3x+y+z+4*s*m=150
25x+20y+10*s*m=250
where x,y,m znd z is unknown and s is given in excel sheet .
i want to find above unknowns by using s data which is given in excel sheet and than plot(x,s):
i have written code in matlab but it gave me error:
clc;
close all;
clear all;
syms x y m z 
myData = readtable('batorrrkhaan.xlsx','Sheet','Taxila-hour')
s = myData.solar_radiation
iThreshold = 200
iKeep = s >= iThreshold
s = s(iKeep)
eqn1=s.*x+4*y-3*z+12*m==100;
eqn2=2*x+3*s.*y+4*z+200*m==200;
eqn3=3*x+y+z+4*s.*m==150;
eqn4=25*x+20*y+10*s.*m==250;
[x,y,t,z]=vpasolve([eqn1, eqn2, eqn3,eqn4],[x,y,t,z]);
x
y
t
z
error is :
z =
Empty sym: 0-by-1
x=
Empty sym: 0-by-1
m=
Empty sym: 0-by-1
y=
Empty sym: 0-by-1

Best Answer

eqn1=s.*x+4*y-3*z+12*m==100;
That does not define one equation: it defines one equation for each value of s.
[x,y,t,z]=vpasolve([eqn1, eqn2, eqn3,eqn4],[x,y,t,z]);
That is length(s) times 4 equations being solved for 4 variables. There are no scalar values of x, y, t, z that are able to satisfy all of the equations simultaneously.
solve() does not know that you mean that you want to solve for x, y, z, t per s value. Using one row of equations per s value will not help: solve() treats the set of equations as if you had done reshape(equations, [], 1)
You need to separate the equations yourself.
[x, y, t, z] = arrayfun(@(E1, E2, E3, E4) vpasolve([E1, E2, E3, E4], [x, y, t, z]), eqn1, eqn2, eqn3, eqn4)
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