Differentiation Equation- result of Derivative

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vu ngothanh 2015-4-16

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评论： vu ngothanh 2015-4-16

I have i math like this:

L=5
x=5*L^2   %x=125

I need to have a result of y; y=diff(x)=50

What is the code that I must type to have result y=50; Thanks in advance

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Answer 1

Mischa Kim 2015-4-16

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Vu, I believe what you are trying to do is this:

 syms y(x)            % define y as a function of x symbolically
 L   = 5;
 y   = 5*x^2;         % define the function y
 dy  = diff(y,x);     % compute its derivative
 dyL = subs(dy,x,L)   % compute the derivative at x = L

You'd need to have access to the Symbolic Math Toolbox to run the code.

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vu ngothanh 2015-4-16

Thank you very much. Thank you for helping me.

vu ngothanh 2015-4-16

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Mr. Mischa Can you help again. I have a same requirement like the one upper. but now is multi variable like this. m,w,k,E,mI,c is constant

      a=(((m*w^2-k)/(E*mI))^2+(c*w/(E*mI))^2)^(1/8);
      b= atan(-c*w/(m*w^2-k))/4+pi/4;
      X=a*cos(b);
      Y=a*sin(b);
      sa=cosh(L*X)*cos(L*Y);
      sb=sinh(L*X)*sin(L*Y);
HOw can I get X',Y',sa',sa'.
Thank you very much