differential equations solution doesnt work

2019 11 21
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更新时间：2019 11 23
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i have for example
syms x y(x)
M4=(R1*x-p*g*pi*0.0810*(x-l1/2)-0.2626*p*g*pi*(x-K1-l2/2)-0.0630*p*g*pi*(x-K2-l3/2)-p*g*pi*((5*x - 19)*(3025*x^2 - 49225*x + 219217))/4704000)/E4/(pi*(b*x+c)^4/64);
%with all the variables known
and i type
ode = diff(y,x,2) == M4;
conds = [y(K4)== 1.7536e-04 Dy(K4)== -2.6143e-04];
ySol(x) = dsolve(ode,conds);
ySol = vpa(simplify(ySol))*10^(6)
yesterday i could solve the equation but today i try it and it continuous running without stopping
Also when i int M4 the result is different from the result yesterday this one does not have and log in it or fantastic number
how can i fix this?

6 个评论
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darova
darova 2019-11-21
Did you try to solve it numerically?
Walter Roberson
Walter Roberson 2019-11-21
Please post values for all of the constants.
To verify: Dy is diff(y) ?
Dimitrios Adam
Dimitrios Adam 2019-11-22
编辑：Walter Roberson 2019-11-22
for some reason when i write
I=vpa((R1*x-p*g*pi*0.0810*(x-l1/2)-0.2626*p*g*pi*(x-K1-l2/2)-0.0630*p*g*pi*(x-K2-l3/2)-p*g*pi*((5*x - 19)*(3025*x^2 - 49225*x + 219217));
and i put I in M4 is working but when i leave it like the original it doesnt work . why?
Also the values are numbers
Walter Roberson
Walter Roberson 2019-11-22
Please post values for all of the constants.
When you do that assignment to I, are you using I/E4/(pi*(b*x+c)^4/64) in place of the M4 you defined before?
Dimitrios Adam
Dimitrios Adam 2019-11-23
编辑：Walter Roberson 2019-11-23
R1=78055; l1 = 1.6; g=9.81; p=7860; K1=l1; K2=3 ; l2=1.4 ; l3=0.8 ;b=-0.5/2.8; c= b*l1-1;
Yes i put it in the place of M4 defined before
Walter Roberson
Walter Roberson 2019-11-23
The expression
I=vpa((R1*x-p*g*pi*0.0810*(x-l1/2)-0.2626*p*g*pi*(x-K1-l2/2)-0.0630*p*g*pi*(x-K2-l3/2)-p*g*pi*((5*x - 19)*(3025*x^2 - 49225*x + 219217));
is missing two ) somewhere. As we are not familiar with the underlying equations, we will have to get you to make the repair.

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