How to assign a value of differential equation?

Not sure how to ask my question, but for example if I have

a= sin(5)+3x

I want to assign its differential value to b, how can I write this?

I can do: diff a

now how to make the answer equal to b b =

Answer 1

[David Sanchez]

http://people.rit.edu/pnveme/pigf/Derivatives/derv_matlab_1.html

Derivatives: Using MATLAB

Using symbolic computation you can obtain analytical derivatives in MATLAB The function is diff(..)

    % analytical derivatives
    syms x y
    y= sin(x); dy = diff(y,'x')
    y=exp(2*x); dy = diff(y)
    % derivative with respect to x is understood

    f = sin(x); g = 2*x^2+3*x + 1;
    y = f*g
    dy =diff(y)  % derivative of product

    u= 2*x + 3; f = sin(u);
    diff(f)   % chain rule

Output from MATLAB

    dy =
    cos(x)
    dy =
    2*exp(2*x)
    y =
    sin(x)*(2*x^2+3*x+1)
    dy =
    cos(x)*(2*x^2+3*x+1)+sin(x)*(4*x+3)
    ans =
    2*cos(2*x+3)