Facing Problem while solving Linear Equations simultaneously

These are my Five Equations

syms a2 a3 a4 a5 a6

EQ_01=a2 +9*a3 + 72*a4 + 540*a5 + 3888*a6 == -121/36000

EQ_02=a3+ a2/12 +9*a4 +72*a5 +540*a6 == -1049/7776000

EQ_03=a4 + (5*a2)/648 + (5*a3)/48 + (25*a5)/3 + (450*a6)/7 == -2987/419904000

EQ_04 =a5 + (7*a2)/8640 + (7*a3)/600 + (7*a4)/60 + (63*a6)/8 == -19789/41990400000

EQ_05 =a6 + a2/10800 + a3/720 + a4/70 + a5/8 == -24163/661348800000

i am trying to solve for the variables a2 , a3, a4 , a5 & a6

here is my code

sol = solve([EQ_01, EQ_02, EQ_03, EQ_04, EQ_05],[a2,a3,a4,a5,a6])

and i got fallowing error

1---Second argument must be a vector of symbolic variables.

2----[eqns, vars] = sym.getEqnsVars(argv{:});

3----[eqns,vars,options] = getEqns(varargin{:});

4----Error in Rayleigh_Ritz_Method (line 104)

sol = solve([EQ_01, EQ_02, EQ_03, EQ_04, EQ_05],[a2,a3,a4,a5,a6]);

Answer 1

[Star Strider]

The only correction required to get this to run is to add the syms declaration —

syms a2 a3 a4 a5 a6

 EQ_01=a2 +9*a3 + 72*a4 + 540*a5 + 3888*a6 == -121/36000 

EQ_01 = 

 
 EQ_02=a3+ a2/12 +9*a4 +72*a5 +540*a6 == -1049/7776000

EQ_02 = 

 
 EQ_03=a4 + (5*a2)/648 + (5*a3)/48 + (25*a5)/3 + (450*a6)/7 == -2987/419904000

EQ_03 = 

 
 EQ_04 =a5 + (7*a2)/8640 + (7*a3)/600 + (7*a4)/60 + (63*a6)/8 == -19789/41990400000

EQ_04 = 

 
 EQ_05 =a6 + a2/10800 + a3/720 + a4/70 + a5/8 == -24163/661348800000

EQ_05 = 

 
  sol = solve([EQ_01, EQ_02, EQ_03, EQ_04, EQ_05],[a2,a3,a4,a5,a6])

sol = struct with fields:
    a2: -265660443171156185011/26563311466141754327040
    a3: 36806947866579283561/39844967199212631490560
    a4: 8376188234952364463/956279212781103155773440
    a5: -76519827268723512571/14344188191716547336601600
    a6: 21255507574645885373/143441881917165473366016000

Note that the error message flagged exactly that problem (that the symbolic variables had not been declared first).

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[inzamam shoukat]

issue not resolved same error came again

[Steven Lord]

Let's make sure you're calling the correct solve function. What does this command show when you run it in your MATLAB session?

which -all solve

/MATLAB/toolbox/pde/@femodel/solve.m            % femodel method
/MATLAB/toolbox/symbolic/symbolic/@sym/solve.m  % sym method

[inzamam shoukat]

>> which -all solve

D:\Installation Software\matlab\toolbox\symbolic\symbolic\@sym\solve.m % sym method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgdivexpr\solve.m % cgdivexpr method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgexpr\solve.m % cgexpr method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgfeature\solve.m % cgfeature method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgsubexpr\solve.m % cgsubexpr method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgvalue\solve.m % cgvalue method

D:\Installation Software\matlab\toolbox\mbc\mbcexpr\@cgvariable\solve.m % cgvariable method

[Star Strider]

It works here (R2024a) and should also work in all recent versions/releases.

Copy and paste this as the first line of your code:

syms a2 a3 a4 a5 a6

so the entire code is now:

syms a2 a3 a4 a5 a6

EQ_01=a2 +9*a3 + 72*a4 + 540*a5 + 3888*a6 == -121/36000

EQ_02=a3+ a2/12 +9*a4 +72*a5 +540*a6 == -1049/7776000

EQ_03=a4 + (5*a2)/648 + (5*a3)/48 + (25*a5)/3 + (450*a6)/7 == -2987/419904000

EQ_04 =a5 + (7*a2)/8640 + (7*a3)/600 + (7*a4)/60 + (63*a6)/8 == -19789/41990400000

EQ_05 =a6 + a2/10800 + a3/720 + a4/70 + a5/8 == -24163/661348800000

sol = solve([EQ_01, EQ_02, EQ_03, EQ_04, EQ_05],[a2,a3,a4,a5,a6])

That should work, as it does again here —

syms a2 a3 a4 a5 a6
EQ_01=a2 +9*a3 + 72*a4 + 540*a5 + 3888*a6 == -121/36000;
EQ_02=a3+ a2/12 +9*a4 +72*a5 +540*a6 == -1049/7776000;
EQ_03=a4 + (5*a2)/648 + (5*a3)/48 + (25*a5)/3 + (450*a6)/7 == -2987/419904000;
EQ_04 =a5 + (7*a2)/8640 + (7*a3)/600 + (7*a4)/60 + (63*a6)/8 == -19789/41990400000;
EQ_05 =a6 + a2/10800 + a3/720 + a4/70 + a5/8 == -24163/661348800000;
sol = solve([EQ_01, EQ_02, EQ_03, EQ_04, EQ_05],[a2,a3,a4,a5,a6])

sol = struct with fields:
    a2: -265660443171156185011/26563311466141754327040
    a3: 36806947866579283561/39844967199212631490560
    a4: 8376188234952364463/956279212781103155773440
    a5: -76519827268723512571/14344188191716547336601600
    a6: 21255507574645885373/143441881917165473366016000

format longE

a2 =  double(sol.a2)

a2 = 
    -1.000102880658436e-02

a3 =  double(sol.a3)

a3 = 
     9.237540009144899e-04

a4 =  double(sol.a4)

a4 = 
     8.759144947417897e-06

a5 =  double(sol.a5)

a5 = 
    -5.334552659655709e-06

a6 =  double(sol.a6)

a6 = 
     1.481820183237729e-07

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[inzamam shoukat]

thanks now its working

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

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