how to use imported data in matlab equations?

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

Answer 1

[Walter Roberson]

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)

[Engineer Batoor khan mummand]

let suppose s has values in range of (J2:J100).

i want to find values of x,y,m and z by using data of s which is import from excel.

[Engineer Batoor khan mummand]

Dear Walter Reberson:

s values we will import from below excel file and other four unknowns we will find from equations than we plot(x,s).

[Engineer Batoor khan mummand]

i need solution of x,y,m and z for each value of s.

than i want to plot(x,s).

[Walter Roberson]

Okay, so read the s data in using readtable or xlsread() . And then proceed from just after your code line

s = myData.solar_radiation

but with the change I show here to use arrayfun.

[Engineer Batoor khan mummand]

thanks from your reply W.R.

if you give some information about E1,E2,E3 and E4 which yu have written in last comment.

this is my code what should i include ?

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
plot(x,s)
hold on
plot(y,s)
hold on
plot(z,s)

[Engineer Batoor khan mummand]

Hi Walter:

the only confusion i have is E1,E2,E3,and E4 in below equation:

[x, y, t, z] = arrayfun(@(E1, E2, E3, E4) vpasolve([E1, E2, E3, E4], [x, y, t, z]), eqn1, eqn2, eqn3, eqn4).

should i put equations instead of E1,E2,E3 and E4 or i should put variables .

thank you so much .

[Engineer Batoor khan mummand]

dear Walter:

this is error :

Error using arrayfun

All of the input arguments must be of the same size and shape.

Previous inputs had size 1 in dimension 1. Input #3 has size 2891

Error in neww (line 15)

[x,y,t,z] = arrayfun(@(x,s)vpasolve([s*x+4*y-3*z+12*t-100, 2*x+3*s.*y+4*z+200*t-200, 3*x+y+z+4*s.*t-150,25*x+20*y+10*s.*t-250]), [x, y, t, z],

eqn1, eqn2, eqn3, eqn4)

thanks

[Walter Roberson]

E1, E2, E3, E4 are argument names for the anonymous function.

[x, y, z, m] = arrayfun(@(E1, E2, E3, E4) vpasolve([E1, E2, E3, E4], [x, y, z, m]), eqn1, eqn2, eqn3, eqn4);

is nearly the same as:

xout = zeros(size(eqn1), 'sym');
yout = zeros(size(eqn1), 'sym');
zout = zeros(size(eqn1), 'sym');
mout = zeros(size(eqn1), 'sym');
for K = 1 : numel(eqn1)
    E1 = eqn1(K);
    E2 = eqn2(K);
    E3 = eqn3(K);
    E4 = eqn4(K);
    [xout(K), yout(K), zout(K), mout(K)] = vpasolve([E1, E2, E3, E4], [x, y, z, m]);
end
x = xout; y = yout; z = zout; m = mout;
clear E1 E2 E3 E4 K xout yout zout mout

During execution of the anonymous function, the first parameter passed to the anonymous function is known by the name E1, the second parameter is known by E2, the third parameter is known by E3, the fourth parameter is known as E4. The body of the anonymous function is executed with those values.

E1, E2, E3, E4 have no independent existence: they stand in for "what was passed as the first parameter", "what was passed as the second parameter" and so on.

[Walter Roberson]

That approach with vpasolve is just too slow. Here is a much faster version:

if ispc()
  filename = 'batorrrkhaan.xlsx';
  varname = 'solar_radiation';
else
  filename = 'Taxila_TMY1.xlsx';
  varname = 'Direct normal Radiation [Wh/m^2]';
end

syms x y m z 
myData = readtable(filename, 'Sheet', 'Taxila-hour', 'PreserveVariableNames', true);
s = myData.(varname);
iThreshold = 200;
iKeep = s >= iThreshold;
s = s(iKeep);

syms S
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;
sol = solve([eqn1, eqn2, eqn3, eqn4], [x, y, z, m]);

x = double(subs(sol.x, S, s));
y = double(subs(sol.y, S, s));
z = double(subs(sol.z, S, s));
m = double(subs(sol.m, S, s));

I had to guess about which variable name in the file you posted corresponded to solar radiation.

You will need to adjust the filename and varname for your actual situation.

[Engineer Batoor khan mummand]

thank you so much for your concentration :

i will try above code .

[Engineer Batoor khan mummand]

Error using readtable (line 198)

Invalid parameter name: PreserveVariableNames.

Error in teching (line 10)

myData = readtable(filename, 'Sheet', 'Taxila-hour', 'PreserveVariableNames', true);

PreserveVariableNames ?

[Walter Roberson]

Either you have a broken MATLAB installation or else you forgot to tell us that you using an old release of MATLAB.

Remove the 'PreserveVariableNames', true option from the call. You may need to adjust the name in the 'varname' assignment, such as to 'DiffuseHorizontalRadiation_Wh_m_2_'

[Engineer Batoor khan mummand]

thanks you so much Dear Walter reberson:

i have no words about you , you have solved my problem.

once again thank you so much .