Error while converting a HUGE symbolic equation to double

[sgvaibhav]

Hi.
I will try to simplify my question to make it clear.

I perform huge calculations worth 70 lines. Beginning by syms x and y.

I get two functions/paramters 'Wnet' and 'SFC' in terms of x and y (VERY HUGE EQUATION)Now i want to plot a very complicated 2D graph.

The script below allows me to plot in 2D but for that, i have to first run first script, get Wnet and SFC and then copy the values and make another function in another script to plot.

clear
for i=1:6;
    
    x(i)=5.*i;
    
    for j=1:5;
        
        y(j)=1000+(100*j);
                        
        %i  ran the first script, copied this from output and pasted here
        x1(i,j)=(99.*((57443.*((4018.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./5 - (57443.*y(j))./50 + (2894969.*x(i).^(200./623))./50))./(50.*((57443.*y(j))./50 - 41160000)) + 57443./50).*(y(j) - y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984)))./100 + (99.*(y(j) - y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984)).*((57443.*((4018.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./5 - (57443.*y(j))./50 + (2894969.*x(i).^(200./623))./50))./(50.*((57443.*y(j))./50 - 41160000)) - (57443.*((57443.*y(j))./50 - (57443.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./50))./(50.*((57443.*y(j))./50 - 41160000)) + 57443./50))./100 - (2894969.*x(i).^(200./623))./10 + 2894969./10;

          % i copied this from output of first script and pasted here
        y1(i,j)=-(((57443.*y(j))./50 - (57443.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./50)./((57443.*y(j))./50 - 41160000) - ((4018.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./5 - (57443.*y(j))./50 + (2894969.*x(i).^(200./623))./50)./((57443.*y(j))./50 - 41160000))./((99.*((57443.*((4018.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./5 - (57443.*y(j))./50 + (2894969.*x(i).^(200./623))./50))./(50.*((57443.*y(j))./50 - 41160000)) + 57443./50).*(y(j) - y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984)))./100 + (99.*(y(j) - y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984)).*((57443.*((4018.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./5 - (57443.*y(j))./50 + (2894969.*x(i).^(200./623))./50))./(50.*((57443.*y(j))./50 - 41160000)) - (57443.*((57443.*y(j))./50 - (57443.*y(j).*(66875./(57036.*x(i))).^(2528214091580831./18014398509481984))./50))./(50.*((57443.*y(j))./50 - 41160000)) + 57443./50))./100 - (2894969.*x(i).^(200./623))./10 + 2894969./10);
        
        x2=x1';
        y2=y1';
                
    end
    
end
plot(x1,y1,x2,y2)

This works, However this code is very inconvenient since i have to copy the big output from first script, change x to x(i), y to y(j), * to .* , / to ./ and ^ to .^ and then i have to paste to second script to plot the graph.Instead i combined to make one big script to directly plot the graph (trying to convert the symbolic equation into double), however i get an error to convert symbolic equation to double. Here is is the second half of the big code, which has the error.

%internal memory from computing the last 70 lines
% (stored internally) Wnet=(99*((57443*((4018*y*(66875/(57036*x))^(2528214091580831/18014398509481984))/5 - (57443*y)/50 + (2894969*x^(200/623))/50))/(50*((57443*y)/50 - 41160000)) + 57443/50)*(y - y*(66875/(57036*x))^(2528214091580831/18014398509481984)))/100 + (99*(y - y*(66875/(57036*x))^(2528214091580831/18014398509481984))*((57443*((4018*y*(66875/(57036*x))^(2528214091580831/18014398509481984))/5 - (57443*y)/50 + (2894969*x^(200/623))/50))/(50*((57443*y)/50 - 41160000)) - (57443*((57443*y)/50 - (57443*y*(66875/(57036*x))^(2528214091580831/18014398509481984))/50))/(50*((57443*y)/50 - 41160000)) + 57443/50))/100 - (2894969*x^(200/623))/10 + 2894969/10;
% (stored internally) SFC=-(((57443.*y)./50 - (57443.*y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984))./50)./((57443.*y)./50 - 41160000) - ((4018.*y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984))./5 - (57443.*y)./50 + (2894969.*x.^(200./623))./50)./((57443.*y)./50 - 41160000))./((99.*((57443.*((4018.*y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984))./5 - (57443.*y)./50 + (2894969.*x.^(200./623))./50))./(50.*((57443.*y)./50 - 41160000)) + 57443./50).*(y - y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984)))./100 + (99.*(y - y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984)).*((57443.*((4018.*y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984))./5 - (57443.*y)./50 + (2894969.*x.^(200./623))./50))./(50.*((57443.*y)./50 - 41160000)) - (57443.*((57443.*y)./50 - (57443.*y.*(66875./(57036.*x)).^(2528214091580831./18014398509481984))./50))./(50.*((57443.*y)./50 - 41160000)) + 57443./50))./100 - (2894969.*x.^(200./623))./10 + 2894969./10);

for i=1:6;
    
    x(i)=5.*i;
    
    for j=1:5;
        
        y(j)=1000+(100*j);
                        
        x1=double(Wnet);              %THE ERROR CODE
        y1=double(SFC);                %THE ERROR CODE
        
        x2=x1';
        y2=y1';
                        
    end
    
end
plot(x1,y1,x2,y2)

However when i run this, i get the error

? Error using ==> mupadmex
Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Error in ==> sym.sym>sym.double at 936
Xstr = mupadmex('symobj::double', S.s, 0);

Error in ==> Working at 14
x1=double(Wnet);Help me =)

If you are still confused with the question, let me know, i will try to clarify it more.

 

[NateD]

The answer to your question is to use the "vpa" function instead of the "double" function. The vpa function can be used to convert symbolic equations into double-precision values that can be used for plotting. For example, you can use the following code to convert your Wnet and SFC equations into double precision values: x1 = vpa(Wnet);y1 = vpa(SFC);You can then use the x1 and y1 values to plot your graph.