Items tagged with diff

hi .in substuting in ode equation i encounter with error

Error, (in eval/diff) invalid input: diff received (f1[i+1, i]-2*f1[i, i]+f1[i-1, i])/h^2, which is not valid for its 2nd argument

please help me

thanksh_2.5_eq4.mw
 

 

restart; with(DEtools); with(plots); interface(rtablesize = 25); ode1 := -P1*(diff(f1(x, y), x, x, x, x, x, x)+diff(f1(x, y), y, y, y, y, y, y)+3*(diff(f1(x, y), x, x, x, x, y, y))+3*(diff(f1(x, y), x, x, y, y, y, y)))+P2*(diff(f1(x, y), x, x, x, x)+diff(f1(x, y), y, y, y, y)+2*(diff(f1(x, y), x, x, y, y)))-N_x*(diff(f1(x, y), x, x))-N_y*(diff(f1(x, y), y, y)); F1xx := i, proc (j) options operator, arrow; (f1[i+1, j]-2*f1[i, j]+f1[i-1, j])/h^2 end proc; F1yy := i, proc (j) options operator, arrow; (f1[i, j+1]-2*f1[i, j]+f1[i, j-1])/hy^2 end proc; F1xxxx := i, proc (j) options operator, arrow; (f1[i+2, j]-4*f1[i+1, j]+6*f1[i, j]-4*f1[i-1, j]+f1[i-2, j])/h^4 end proc; F1yyyy := i, proc (j) options operator, arrow; (f1[i, j+2]-4*f1[i, j+1]+6*f1[i, j]-4*f1[i, j-1]+f1[i, j-2])/hy^4 end proc; F1xxxxxx := i, proc (j) options operator, arrow; (f1[i+3, j]-6*f1[i+2, j]+15*f1[i+1, j]-20*f1[i, j]+15*f1[i-1, j]-6*f1[i-2, j]+f1[i-3, j])/h^6 end proc; F1yyyyyy := i, proc (j) options operator, arrow; (f1[i, j+3]-6*f1[i, j+2]+15*f1[i, j+1]-20*f1[i, j]+15*f1[i, j-1]-6*f1[i, j-2]+f1[i, j-3])/hy^6 end proc; F1xxyyyy := i, proc (j) options operator, arrow; (f1[i-1, j-2]-4*f1[i-1, j-1]+6*f1[i-1, j]-4*f1[i-1, j+1]+f1[i-1, j+2]-2*f1[i, j-2]+8*f1[i, j-1]-12*f1[i, j]+8*f1[i, j+1]-2*f1[i, j+2]+f1[i+1, j-2]-4*f1[i+1, j-1]+6*f1[i+1, j]-4*f1[i+1, j+1]+f1[i+1, j+2])/(hy^4*h^2) end proc; F1yyxxxx := i, proc (j) options operator, arrow; (f1[i-2, j-1]-2*f1[i-2, j]+f1[i-2, j+1]-4*f1[i-1, j-1]+8*f1[i-1, j]-4*f1[i-1, j+1]+6*f1[i, j-1]-12*f1[i, j]+6*f1[i, j+1]-4*f1[i+1, j-1]+8*f1[i+1, j]-4*f1[i+1, j+1]+f1[i+2, j-1]-2*f1[i+2, j]+f1[i+2, j+1])/(h^4*hy^2) end proc; eq := simplify(eval(ode1, {diff(f1(x, y), x, x) = F1xx(i, j), diff(f1(x, y), y, y) = F1yy(i, j), diff(f1(x, y), x, x, x, x) = F1xxxx(i, j), diff(f1(x, y), y, y, y, y) = F1yyyy(i, j), diff(f1(x, y), x, x, x, x, x, x) = F1xxxxxx(i, j), diff(f1(x, y), x, x, x, x, y, y) = F1yyxxxx(i, j), diff(f1(x, y), x, x, y, y, y, y) = F1xxyyyy(i, j), diff(f1(x, y), y, y, y, y, y, y) = F1yyyyyy(i, j)}))

Error, (in eval/diff) invalid input: diff received (f1[i+1, i]-2*f1[i, i]+f1[i-1, i])/h^2, which is not valid for its 2nd argument

 

NULL

 

expand(%)

i

(1)

simplify(4*h^4*f3[i]*f4[i]*%)

4*h^4*f3[i]*f4[i]*i

(2)

diff(f1(x, y), x, x, y, y, y, y)

diff(diff(diff(diff(diff(diff(f1(x, y), x), x), y), y), y), y)

(3)

``

``

NULL


 

Download h_2.5_eq4.mw

 

Dear all:

I have used the "diff" command in Maple to help me derive a huge and very long function, and now I want to convert this huge expression from Maple to Matlab format, for example, into a Matlab .m file. The format of this expression in Maple is very different from Matlab.

So could you help me with this problem?

Thank you all.

Hello, I have a function defined as

                                                   g :=  (x, y)->diff(u1(x, y), x, x)+diff(u2(x, y), x, y). 

I want to define another function as follows

                                                           f :=  (y) ->subs(x = 0, g(x, y)) ,

Now, when I want to calculate numerical values for the new function f(0), f(0.1), f(0.2),..... and so on. The following massage appear

Error, (in f) invalid input: diff received 0, which is not valid for its 2nd argument.

What is the problem here.

Amr
 

 

 

EDIT: My question has been  answered below

 

Hello,

Lets' say I have the equation L:

 

L= 

I want to take the partial derivative of L to diff(theta2(t), t). 

Maple doesn't allow me to do this: diff(L, diff(theta2(t),t));

How can I solve this problem?

 

I hope someone can help me. Thanks in advance!

Loïc

Hi everybody;

I have a problem with Physics[diff] command. When I run the following code, error messages appear where the Physics[diff] command exist. What is the source of error? How can I fix it?

Thanks in advance

Q1.mw

I wish to define a function which is the derivative of another function.

> f:=(x)->x^2:

> g:=(x)->diff(f(x),x):

> g(x);

2 x

> f(2);

4

> g(2);
Error, (in g) invalid input: diff received 2, which is not valid for its 2nd argument

 

I cannot find a way in which I can define the function g, using the functional operator, so that I can actually evaluate g(x).

 

How can I do this?

 

#Hello people in Mapleprimes,

#After

restart;interface(typesetting=extended);

diff(f(x),x);

#shows f'(x).

#But,

diff(f(t1),t1);

#shows just df(t1)/dt1, not f'(t).

#Can't I show f'(t1) not df(t1)/dt1?

#Is this a way peculiar to Maple?

#I hope someone could give me some hints.

 

#Best wishes.

#taro

 

 

 

 

hi 

how i can apply this differential in maple?

thabks...

 

Hello,

I need to crate a function to be evaluated in a range of values, and this function i would to use in other expression, example:

cel1      "seq(i,i=0.001..2,0.001)"

cel2      "A:=&1";cel1

cel3      "f:=x->diff(KelvinBei(0,x),x)"

cel4      ""B:=map(x->f(x),[A])"

 

This is ok with a lot of function but with diff(KelvinBei(0,x),x) in cel4 show this error "Error,(in f) invalid input:.1e-2, which is not valid for its 2nd argument.

Why??? How can I do??

Hey all,

I want to symbolically differentiate a function and recalculate the result later. Here is what I have tried so far:


restart;

myexp:=dfdb+sthlong

dfdb+sthlong

(1)

b:=<b1(t),b2(t)>;

b := Vector(2, {(1) = b1(t), (2) = b2(t)})

(2)

dfdb:=Physics[diff]~(f(b),b)

dfdb := Vector(2, {(1) = (D(f))(Vector(2, {(1) = b1(t), (2) = b2(t)})), (2) = (D(f))(Vector(2, {(1) = b1(t), (2) = b2(t)}))})

(3)

f:=b->b(1)^2+b(2)

proc (b) options operator, arrow; b(1)^2+b(2) end proc

(4)

eval(myexp);  #actual result

 

 

sthlong+(Vector(2, {(1) = (D(f))(Vector(2, {(1) = b1(t), (2) = b2(t)})), (2) = (D(f))(Vector(2, {(1) = b1(t), (2) = b2(t)}))}))

(5)

dfdb:=Physics[diff]~(f(b),b):

eval(myexp); #expected result

sthlong+(Vector(2, {(1) = 2*b1(t), (2) = 1}))

(6)

 


Download physics_diff.mw

I wonder if this is even possible, or if I missunderstand something. Can you please help me?

 

Thanks

 

Honigmelone

Hello,

 

I'm modeling the simple DC motor system in Maple.
The equations describing the system;

eq1:=J*diff(theta(t),t,t)+b*diff(theta(t),t)=K*i(t):
eq2:=L*diff(i(t),t)+R*i(t)=V(t)-K*diff(theta(t),t):
DCMotor:=[eq1,eq2];

First, I create the system using DiffEquation:

Sys:=DiffEquation(DCMotor,[V(t)],[theta(t)]);

And now I have problem. The input var is V(t) (input voltage) and the output var is theta(t) (position of the rotor).

But I wont to have in output var not position of the rotor but speed of the fotor - diff(theta(t),t)

How to set output var for diff(theta(t),t) (the speed of the motor)?

 

Best

Rariusz

 

Hi

 

I am new to Maple and discovering its features. I was wondering whether it is possible to define a function abstractly, say:

fo:=f(1/x)

and differentiate it, to obtain f'(1/x) (-1/x^2)? Is this possible?

 

Thanks!

Hello :-),

 

How can I differentiate the follwing function:

Cq = Cao*k1*t / [(1+k1*t)*(1+k2*t)]

If want to find the maximum:

dCq/dt = 0

I can solve if of course by hand. The solution is t=1/sqrt(k1*k2)

I tried it with maple, but I got a strange result (see picture). How can I use maple to get the right result?

 

Thank you very much!

 

Dear All

How can we collect coefficient wrt certain differential ration in an expression?

See for detail:


with(PDEtools):

u := a[0]+a[1]*(diff(phi(xi), xi))/phi(xi)

a[0]+a[1]*(diff(phi(xi), xi))/phi(xi)

(1)

-k*(diff(u, `$`(xi, 2)))+alpha*(diff(u, `$`(xi, 3)))

-k*(a[1]*(diff(diff(diff(phi(xi), xi), xi), xi))/phi(xi)-3*a[1]*(diff(diff(phi(xi), xi), xi))*(diff(phi(xi), xi))/phi(xi)^2+2*a[1]*(diff(phi(xi), xi))^3/phi(xi)^3)+alpha*(a[1]*(diff(diff(diff(diff(phi(xi), xi), xi), xi), xi))/phi(xi)-4*a[1]*(diff(diff(diff(phi(xi), xi), xi), xi))*(diff(phi(xi), xi))/phi(xi)^2+12*a[1]*(diff(diff(phi(xi), xi), xi))*(diff(phi(xi), xi))^2/phi(xi)^3-3*a[1]*(diff(diff(phi(xi), xi), xi))^2/phi(xi)^2-6*a[1]*(diff(phi(xi), xi))^4/phi(xi)^4)

(2)

expand(dsubs(diff(phi(xi), `$`(xi, 2)) = -lambda*(diff(phi(xi), xi))-mu*phi(xi), -k*(a[1]*(diff(diff(diff(phi(xi), xi), xi), xi))/phi(xi)-3*a[1]*(diff(diff(phi(xi), xi), xi))*(diff(phi(xi), xi))/phi(xi)^2+2*a[1]*(diff(phi(xi), xi))^3/phi(xi)^3)+alpha*(a[1]*(diff(diff(diff(diff(phi(xi), xi), xi), xi), xi))/phi(xi)-4*a[1]*(diff(diff(diff(phi(xi), xi), xi), xi))*(diff(phi(xi), xi))/phi(xi)^2+12*a[1]*(diff(diff(phi(xi), xi), xi))*(diff(phi(xi), xi))^2/phi(xi)^3-3*a[1]*(diff(diff(phi(xi), xi), xi))^2/phi(xi)^2-6*a[1]*(diff(phi(xi), xi))^4/phi(xi)^4)))

-a[1]*(diff(phi(xi), xi))*alpha*lambda^3/phi(xi)-a[1]*alpha*lambda^2*mu-7*a[1]*(diff(phi(xi), xi))^2*alpha*lambda^2/phi(xi)^2-8*a[1]*(diff(phi(xi), xi))*alpha*lambda*mu/phi(xi)-a[1]*(diff(phi(xi), xi))*k*lambda^2/phi(xi)-2*a[1]*alpha*mu^2-a[1]*k*lambda*mu-12*a[1]*(diff(phi(xi), xi))^3*alpha*lambda/phi(xi)^3-8*a[1]*(diff(phi(xi), xi))^2*alpha*mu/phi(xi)^2-3*a[1]*(diff(phi(xi), xi))^2*k*lambda/phi(xi)^2-2*a[1]*(diff(phi(xi), xi))*k*mu/phi(xi)-6*a[1]*(diff(phi(xi), xi))^4*alpha/phi(xi)^4-2*a[1]*(diff(phi(xi), xi))^3*k/phi(xi)^3

(3)

How ca extract coefficients of fraction (diff(phi(xi), xi))/phi(xi) in (3) ????


Download Coefficients_of_Fractions.mw

Regards

diff(a(t), t) = diff(a(t), t);
diff(b(t),t) = 0;
diff(c(t),t) = -b(t)/a(t);

[diff(rhs(sol[1][2]), a(t)),diff(rhs(sol[1][2]), b(t)),diff(rhs(sol[1][2]), c(t))];
Error, (in VectorCalculus:-diff) invalid input: diff received a(t), which is not valid for its 2nd argument

 

 

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