Unable to convert expression into double array

When I run my code, I keep getting this error: "The following error occurred converting from sym to double: Unable to convert expression into double array."

r=50; 
d=50;
a=12.61; 

syms x
syms y
J=(besselj(0,x*y*a/d))*((1-y^2)^0.5)*y;
B1=int(J, y, [0 1]);

E1=zeros(1,301);
t=0:0.1:30;
for i=1:301
    B=B1*besselj(0,x*r/d)*((x*tanh(x))^0.5)*sin((((9.81/d*t(i)^2)*x)*tanh(x))^0.5)*x;
    E1(i)=vpaintegral(B, x, [0 2000])
end

Answer 1

[Areej Varamban Kallan]

Hi Tommaso,

The variable E1 is defined to be a 'double' array outside the foor loop. The variable B is of symbolic type. In the for loop you are attempting to assign each element of a 'double' array to a symbolic object, which is not correct. Redefine E1 as:

E1 = sym(zeros(1,301));

[Tommaso Attili]

Hi Areej,

Thanks for you help. I'll modify my code. Then to plot E1 versus t is it right:

f=double(E1)
plot(t,f)

Answer 2

[Bo Zhang]

thanks