MATLAB: How to manually insert variables I have declared symbolically into a zero matrix

insert variableMATLABsymbolic manipulatorzeros

I have been trying to insert symbolic variable into a zero matrix.
    clear all
    clc
    syms k1 k2 k3 k4
    global_k1 = zeros(4,4);
    global_k2 = zeros(4,4);
    global_k3 = zeros(4,4);
    global_k4 = zeros(4,4);
    global_k1(1,1) =  k1;
    global_k1(1,2) = -k1;
    global_k1(2,1) = -k1;
    global_k1(2,2) =  k1;
    global_k2(2,2) =  k2;
    global_k2(2,3) = -k2;
    global_k2(3,2) = -k2;
    global_k2(3,3) =  k2;
    global_k3(2,2) =  k3;
    global_k3(2,3) = -k3;
    global_k3(3,2) = -k3;
    global_k3(3,3) =  k3;
    global_k4(2,2) =  k4;
    global_k4(2,4) = -k4;
    global_k4(4,2) = -k4;
    global_k4(4,4) =  k4;
    k_stiff = global_k1+global_k2+global_k3+global_k4;
    disp('The stiffness matrix is: ');
    disp(k_stiff);
It displays the following error when I run the program:
The following error occurred converting from sym to double:
Unable to convert expression into double array.
Error in HW1_1 (line 9)
global_k1(1,1) =  k1;
How should I resolve this error?

Best Answer

>> syms k1 k2 k3 k4
        global_k1 = sym(zeros(4,4));
        global_k2 = sym(zeros(4,4));
        global_k3 = sym(zeros(4,4));
        global_k4 = sym(zeros(4,4));
        global_k1(1,1) =  k1;
        global_k1(1,2) = -k1;
        global_k1(2,1) = -k1;
        global_k1(2,2) =  k1;
        global_k2(2,2) =  k2;
        global_k2(2,3) = -k2;
        global_k2(3,2) = -k2;
        global_k2(3,3) =  k2;
        global_k3(2,2) =  k3;
        global_k3(2,3) = -k3;
        global_k3(3,2) = -k3;
        global_k3(3,3) =  k3;
        global_k4(2,2) =  k4;
        global_k4(2,4) = -k4;
        global_k4(4,2) = -k4;
        global_k4(4,4) =  k4;
        global_k1
        global_k2
        global_k3
        global_k4
        k_stiff = global_k1+global_k2+global_k3+global_k4;
        disp('The stiffness matrix is: ')
        disp(k_stiff);
global_k1 =
[  k1, -k1, 0, 0]
[ -k1,  k1, 0, 0]
[   0,   0, 0, 0]
[   0,   0, 0, 0]
global_k2 =
[ 0,   0,   0, 0]
[ 0,  k2, -k2, 0]
[ 0, -k2,  k2, 0]
[ 0,   0,   0, 0]
global_k3 =
[ 0,   0,   0, 0]
[ 0,  k3, -k3, 0]
[ 0, -k3,  k3, 0]
[ 0,   0,   0, 0]
global_k4 =
[ 0,   0, 0,   0]
[ 0,  k4, 0, -k4]
[ 0,   0, 0,   0]
[ 0, -k4, 0,  k4]
The stiffness matrix is: 
[  k1,               -k1,         0,   0]
[ -k1, k1 + k2 + k3 + k4, - k2 - k3, -k4]
[   0,         - k2 - k3,   k2 + k3,   0]
[   0,               -k4,         0,  k4]
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