how to use imported data in matlab equations?

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Engineer Batoor khan mummand 2020-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/606991-how-to-use-imported-data-in-matlab-equations

评论： Engineer Batoor khan mummand 2020-10-8

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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

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采纳的回答

Walter Roberson 2020-10-7

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/606991-how-to-use-imported-data-in-matlab-equations#answer_507346

在 MATLAB Online 中打开

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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Walter Roberson 2020-10-8

在 MATLAB Online 中打开

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 2020-10-8

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 2020-10-8