Solve function not working

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Joirdan Noronha
Joirdan Noronha 2021-4-1
评论： Walter Roberson 2021-4-1
Hi everyone, I'm really new to Matlab and am struggling to get this code to work, I was hoping for the Wall_thickness and Outer_Diameter variables to output numbers but I've been unsuccessful. Any ideas?
%% Parameters
Outer_Diameter = 2;
Unit_Cell_Size = 4;
Material_Density = 4.41;
Lattice_Density = 2.8;
%% Calculations
Mass = Lattice_Density*((0.1*Unit_Cell_Size)^3);
Unit_Cell_Volume_cm = Mass/Material_Density;
Unit_Cell_Volume_mm = Unit_Cell_Volume_cm/0.001;
syms Wall_thickness Outer_Diameter
Equation1 = ((pi*(Outer_Diameter/2)^2)*Unit_Cell_Size)-((pi*(Outer_Diameter/2)^2)*Outer_Diameter);
Equation2 = ((pi*((Outer_Diameter/2)-Wall_thickness)^2)*Unit_Cell_Size)-((pi*((Outer_Diameter/2)-Wall_thickness)^2)*(Outer_Diameter-(2*Wall_thickness)));
solve(Equation1,Equation2);

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Walter Roberson
Walter Roberson 2021-4-1
编辑：Walter Roberson 2021-4-1
Ran in:
%% Parameters
Outer_Diameter = 2;
Unit_Cell_Size = 4;
Material_Density = 4.41;
Lattice_Density = 2.8;
%% Calculations
Mass = Lattice_Density*((0.1*Unit_Cell_Size)^3);
Unit_Cell_Volume_cm = Mass/Material_Density;
Unit_Cell_Volume_mm = Unit_Cell_Volume_cm/0.001;
syms Wall_thickness Outer_Diameter
Equation1 = ((pi*(Outer_Diameter/2)^2)*Unit_Cell_Size)-((pi*(Outer_Diameter/2)^2)*Outer_Diameter);
Equation2 = ((pi*((Outer_Diameter/2)-Wall_thickness)^2)*Unit_Cell_Size)-((pi*((Outer_Diameter/2)-Wall_thickness)^2)*(Outer_Diameter-(2*Wall_thickness)));
sol = solve(Equation1,Equation2);
sol.Outer_Diameter
ans = 
sol.Wall_thickness
ans = 
  3 个评论
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Joirdan Noronha
Joirdan Noronha 2021-4-1
I'm weirdly getting this response
ans =
Empty sym: 0-by-1
ans =
Empty sym: 0-by-1
Walter Roberson
Walter Roberson 2021-4-1
Ran in:
Unit_Cell_Size = 4;
Material_Density = 4.41;
Lattice_Density = 2.8;
%% Calculations
Mass = Lattice_Density*((0.1*Unit_Cell_Size)^3);
Unit_Cell_Volume_cm = Mass/Material_Density;
Unit_Cell_Volume_mm = Unit_Cell_Volume_cm/0.001;
syms Outer_Diameter Wall_thickness
Equation1 = Unit_Cell_Volume_mm == 2*(((pi*(Outer_Diameter/2)^2)*Unit_Cell_Size)-((pi*(Outer_Diameter/2)^2)*Outer_Diameter)-((pi*((Outer_Diameter/2)-Wall_thickness)^2)*Unit_Cell_Size)-((pi*((Outer_Diameter/2)-Wall_thickness)^2)*(Outer_Diameter-(2*Wall_thickness))))+(((pi*(Outer_Diameter/2)^2)*Unit_Cell_Size)-((pi*((Outer_Diameter/2)-Wall_thickness)^2)*Unit_Cell_Size));
Equation2 = ((pi*(Outer_Diameter/2)^2)*Unit_Cell_Size)-((pi*(Outer_Diameter/2)^2)*Outer_Diameter);
Equation3 = ((pi*((Outer_Diameter/2)- Wall_thickness)^2)*Unit_Cell_Size)-((pi*((Outer_Diameter/2)- Wall_thickness)^2)*(Outer_Diameter-(2*Wall_thickness)));
sol = solve(Equation1,Equation2)
sol = struct with fields:
Outer_Diameter: [6×1 sym] Wall_thickness: [6×1 sym]
E3 = subs(Equation3, sol)
E3 = 
vpa(E3)
ans = 
You have three equations in two variables. If you solve the first two equations for the two variables, and substitute those into the third equation, none of the possibilities solve the third equation.
There is no combination of the two variables that can solve all three equations at the same time.

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