## How to extract rhs (right hand side)...

Hello all,

When I tried to extract the RHS of the answer from 'solve()' command, the attempt failed.

 > restart;
 > sys := U__s^2 = ((1+sigma)*U__T2N - u__rN * U__T2N/(1+sigma))^2+(u__xN * U__T2N/(1+sigma))^2;
 (1)
 > answer := solve( sys, {U__T2N} );
 (2)
 (3)
 >

Perhaps, the failure might be related to the fact that the equation is contained in curly brackets, but I could not come up with a solution.

Please let me have a chance to learn the way to do the 'rhs()' operation in the correct way.

Thank you,

In Kwon Park

## Vector functions: defining, differentiating, plott...

I want to define a vector function, then plot it, differentiate it, etc.

The best I've been able to do so far is to define it two different ways: one for evaluating, one for symbolic manipulation

with(plots): with(VectorCalculus):
r:= < cos(t), sin(t), t >;  # symbolic version of function, for example to take derivative
# returns derivative,
diff(r,t);
rf := (t)->evalf( < cos(t), sin(t), t > );   # returns numerical value of function
# we use numerical version to plot
rCurve := spacecurve( rf(t), t = -1 .. 1 );
# But how to return value of derivative?? Next line doesn't work.
df := (t)->evalf( diff(r,t) );

But how do I plot the derivative? The last line doesn't work. I've tried various variations but no luck.

I don't think this approach is write (why define two different ways?) but haven't been able to figure out how to do it.

Various online docs haven't helped.

## dsolve gives solution with no y(x) in it. What do...

I was trying to compare my solution with Maple on this ode, when I noticed Maple gives solution with no y(x)= in it.

```restart;
ode:=(y(x)-x*diff(y(x),x))/(y(x)^2+diff(y(x),x))=(y(x)-x*diff(y(x),x))/(1+x^2*diff(y(x),x));
sol:=dsolve(ode)
```

When there is more than one solution, Maple write y(x) on each. For an example

`dsolve(diff(y(x),x)^2=x)`

How to explain this output?

Maple 2020.1

## another problem with odetest. Verification depends...

I think I've seen such a problem before but thought it was fixed.

Here is an example, where depending on what one calls the constant of integration, maple can or not, verify the solution of the ode.

This should not happen.

When calling the constant of integration C[1] or _C Maple does not verify the solution. Only when using _C1 it does.

This is a problem, since I do not use _C1 or _C2  in my solution (so not to conflict with Maple's), I use C[1] and C[2].

Is there a workaround for this?

Example 1

```ode:=diff(z(x),x)+z(x)*cos(x)=z(x)^n*sin(2*x);
mysol:=z(x) = 1/((_C1*exp(sin(x)*(n - 1))*n - _C1*exp(sin(x)*(n - 1)) + 2*sin(x)*n - 2*sin(x) + 2)/(n - 1))^(1/(n - 1));
odetest(mysol,ode);

0```

Now I just changed _C1 to C[1]

```restart;
ode:=diff(z(x),x)+z(x)*cos(x)=z(x)^n*sin(2*x);
mysol:=z(x) = 1/(( C[1]*exp(sin(x)*(n - 1))*n - C[1]*exp(sin(x)*(n - 1)) + 2*sin(x)*n - 2*sin(x) + 2)/(n - 1))^(1/(n - 1));
odetest(mysol,ode);
```

and I get 2 pages full of stuff thrown at the screen. Same when using C as constant of integration.

I could change my C[1] and C[2] to _C1 and _C2 each time just before calling odetest as workaround.

But would like to ask if this is supposed to happen and why it happens. I depend on odetest alot, as I use it to tell me if my solution is correct or not and I do not want false negatives.

I have found additional ones. May be these will help locate the problem

Example 2

```restart;
ode:=diff(y(x),x) = (1+x+y(x))^(1/2);
mysol1:=y(x) = LambertW(-exp(-x/2 - 1 + C[1]/2))^2 + 2*LambertW(-exp(-x/2 - 1 + C[1]/2)) - x:
odetest(mysol1,ode);
```

gives

```restart;
ode:=diff(y(x),x) = (1+x+y(x))^(1/2):
mysol2:=y(x) = LambertW(-exp(-x/2 - 1 + _C1/2))^2 + 2*LambertW(-exp(-x/2 - 1 + _C1/2)) - x:
odetest(mysol2,ode);
```

Example 3

```restart;
ode:=diff(y(x),x) = f(x)*y(x)+g(x)*y(x)^k:
mysol1:=y(x) = (-exp(-(k - 1)*Int(f(x), x))*(int(g(x)*exp((k - 1)*Int(f(x), x)), x)*k - int(g(x)*exp((k - 1)*Int(f(x), x)), x) - C[1]))^(-1/(k - 1)):
odetest(mysol1,ode);

#long output is given```

Changing C[1] to _C1 gives 0 right away

```restart;
ode:=diff(y(x),x) = f(x)*y(x)+g(x)*y(x)^k:
mysol2:=y(x) = (-exp(-(k - 1)*Int(f(x), x))*(int(g(x)*exp((k - 1)*Int(f(x), x)), x)*k - int(g(x)*exp((k - 1)*Int(f(x), x)), x) - _C1))^(-1/(k - 1)):
odetest(mysol2,ode);

0```

Example 4

```restart;
ode:=3*y(x)*diff(y(x),x)+5*cot(x)*cot(y(x))*cos(y(x))^2 = 0:
mysol1:=y(x) = RootOf(10*ln(sin(x))*cos(_Z)^2 - 3*cos(_Z)*sin(_Z) + 30*C[1]*cos(_Z)^2 + 3*_Z):
odetest(mysol1,ode);
```

Gives pages long output. Changing C[1] to _C1 gives zero

```restart;
ode:=3*y(x)*diff(y(x),x)+5*cot(x)*cot(y(x))*cos(y(x))^2 = 0:
mysol2:=y(x) = RootOf(10*ln(sin(x))*cos(_Z)^2 - 3*cos(_Z)*sin(_Z) + 30*_C1*cos(_Z)^2 + 3*_Z):
odetest(mysol2,ode);

0```

Example 5

```restart;
ode:=x*(x-a*y(x))*diff(y(x),x) = y(x)*(y(x)-a*x);
mysol1:=y(x) = exp((-a + 1)*RootOf(x*exp(ln(x)*a + _Z*a + C[1]*a + C[1]) + exp(ln(x)*a + _Z*a + C[1]*a - _Z + C[1])*x - 1) - ln(x)*a - C[1]*(a + 1)):
odetest(mysol1,ode);
```

gives

Changing C[1] to _C1 gives zero

```restart;
ode:=x*(x-a*y(x))*diff(y(x),x) = y(x)*(y(x)-a*x);
mysol2:=y(x) = exp((-a + 1)*RootOf(x*exp(ln(x)*a + _Z*a + _C1*a + _C1) + exp(ln(x)*a + _Z*a + _C1*a - _Z + _C1)*x - 1) - ln(x)*a - _C1*(a + 1)):
odetest(mysol2,ode);

0```

Example 6

```restart;
ode:=x*diff(y(x),x)^2-a*y(x)*diff(y(x),x)+b = 0:
mysol1:=y(x) = x*RootOf(2*x*_Z^2*a - 2*C[1]*_Z^((2*a - 1)/(a - 1))*a - x*_Z^2 + C[1]*_Z^((2*a - 1)/(a - 1)) - b)/a + b/(RootOf(2*x*_Z^2*a - 2*C[1]*_Z^((2*a - 1)/(a - 1))*a - x*_Z^2 + C[1]*_Z^((2*a - 1)/(a - 1)) - b)*a):
odetest(mysol1,ode);
```

gives many pages of output. Changing C[1] to _C1 gives zero

```restart;
ode:=x*diff(y(x),x)^2-a*y(x)*diff(y(x),x)+b = 0:
mysol2:=y(x) = x*RootOf(2*x*_Z^2*a - 2*_C1*_Z^((2*a - 1)/(a - 1))*a - x*_Z^2 + _C1*_Z^((2*a - 1)/(a - 1)) - b)/a + b/(RootOf(2*x*_Z^2*a - 2*_C1*_Z^((2*a - 1)/(a - 1))*a - x*_Z^2 + _C1*_Z^((2*a - 1)/(a - 1)) - b)*a):
odetest(mysol2,ode);

0```

and more. I think the above should hopefully help locate the issue.

Maple 2020.1 with Physics 708

## General Solution of ODE with Arbitrary Constant Co...

The general solution of x2y'' + 3xy' + λy = 0 is (from Example 4 here)

Why does `dsolve(x^2*diff(y(x), x, x) + 3*x*diff(y(x), x) + lambda*y(x) = 0)` give only the third case instead of the whole solution?

## How to solve system of equations under the conditi...

How to find all solutions [xi,yi] to the following system of equations

x3y=1

y-sin(12x)=0

which satisfies condition 1,2<x<2

## Animated four-leaved rose...

I want to show the animation of the polar equation r=cos(2theta) be plotted from theta=0 to 2pi

## Find positive integer solutions of equations for a...

Hello,The system of equations is as follows：

I'd like to find all integer solutions in [1,20], when I use isolve ,the results are not good.  Since at least one variable is equal to 0 in evey solution.

{isolve}({a+b+c=a1+b1+c1, a^2+b^2+c^2=(a1)^2+(b1)^2+(c1)^2,a*b*c=2*a1*b1*c1})

In maple I did not  want to use less efficient for-loop like C programing as following.

#include <math.h>
#include <stdio.h>
void main()
{
long int a,b,c,d,e,f;
for(a=1;a<20;a++)
{
for(b=1;b<20;b++)
{
for(c=1;c<20;c++)
{
for(d=1;d<20;d++)
{
for(e=1;e<20;e++)
{
for(f=1;f<20;f++)
{
if(a+b+c==d+e+f&&a*a+b*b+c*c==d*d+e*e+f*f&&a*b*c==2*d*e*f)                                             printf("a=%d,b=%d,c=%d,d=%d,e=%d,f=%d\n",a,b,c,d,e,f);
}
}
}
}
}
}
}
a=3,b=5,c=16,d=1,e=8,f=15
a=3,b=5,c=16,d=1,e=15,f=8
a=3,b=5,c=16,d=8,e=1,f=15
a=3,b=5,c=16,d=8,e=15,f=1
a=3,b=5,c=16,d=15,e=1,f=8
a=3,b=5,c=16,d=15,e=8,f=1
a=3,b=16,c=5,d=1,e=8,f=15
a=3,b=16,c=5,d=1,e=15,f=8
a=3,b=16,c=5,d=8,e=1,f=15
a=3,b=16,c=5,d=8,e=15,f=1
a=3,b=16,c=5,d=15,e=1,f=8
a=3,b=16,c=5,d=15,e=8,f=1
a=5,b=3,c=16,d=1,e=8,f=15
a=5,b=3,c=16,d=1,e=15,f=8
a=5,b=3,c=16,d=8,e=1,f=15
a=5,b=3,c=16,d=8,e=15,f=1
a=5,b=3,c=16,d=15,e=1,f=8
a=5,b=3,c=16,d=15,e=8,f=1
a=5,b=16,c=3,d=1,e=8,f=15
a=5,b=16,c=3,d=1,e=15,f=8
a=5,b=16,c=3,d=8,e=1,f=15
a=5,b=16,c=3,d=8,e=15,f=1
a=5,b=16,c=3,d=15,e=1,f=8
a=5,b=16,c=3,d=15,e=8,f=1
a=16,b=3,c=5,d=1,e=8,f=15
a=16,b=3,c=5,d=1,e=15,f=8
a=16,b=3,c=5,d=8,e=1,f=15
a=16,b=3,c=5,d=8,e=15,f=1
a=16,b=3,c=5,d=15,e=1,f=8
a=16,b=3,c=5,d=15,e=8,f=1
a=16,b=5,c=3,d=1,e=8,f=15
a=16,b=5,c=3,d=1,e=15,f=8
a=16,b=5,c=3,d=8,e=1,f=15
a=16,b=5,c=3,d=8,e=15,f=1
a=16,b=5,c=3,d=15,e=1,f=8
a=16,b=5,c=3,d=15,e=8,f=1

Does Maple have more good ways to solve that?

## How to minimize the usage of memory using Grid:-Se...

Hello

I had to save previous results of a calculation to files as the number of elements is too big for my computer to handle in one go.   Here it is an idea of what I am doing to read the files and perform the calculations.

```mainproc:=proc(arg1,arg2,arg3,arg4) ... end proc:

Grid:-Set(mainproc):
Grid:-Set(arg2,arg3,arg4):   #  They don't change ever.

for i from 1 to number_of_files do
Grid:-Set(arg1):
ans:=Grid:-Seq(mainproc(arg1[i],arg2,arg3,arg4),i=1..numelems(arg1))):
Grid:-Wait():
save ans, ....:
unassign('arg1'):
unassign('ans'):
gc():  # An attempt
end do:

```

The actual code works but, for every step in the loop, the memory used by Maple increases by a certain amount that seems to be mostly related to arg1 (as if arg1 is piling up from iteration to iteration).

I read some of the earlier posts on a similar subject dated 5 to 10 years old.  I wonder if there is something new that can be done to minimize the usage of memory.

Many thanks

Ed

## How do I get the sum of a column in a matrix?...

I have a simple matrix, 11 rows x 3 columns, with header row.

I multiply column 1 and 2 to get

Now, I just want to add up these elements, but 'sum' doesn't work 'Sum' doesn't work either. Is there a simpel way to do this?

 >
 (1)
 >
 (2)
 >
 (3)
 >
 >

## Classification of conic sections...

I must do some formula manipulation

Classification of conic sections

 > restart; with(student):
 > A*x^2+B*y^2+C*x+D*y+E=0;
 (1)
 > f:= A*x^2+B*y^2+C*x+D*y+E;
 (2)
 > completesquare(f, x);
 (3)
 > f:= A*x^2+B*y^2+C*x+D*y+E;
 (4)
 > ans:=Student[Precalculus][CompleteSquare]( (4), [y] );
 (5)
 > ans1:=Student[Precalculus][CompleteSquare]( (4), [x] );
 (6)
 > ans+ans1;
 (7)
 > B*(y + D/(2*B))^2 + A*x^2 + C*x + 2*E - D^2/(4*B) + A*(x + C/(2*A))^2 - C^2/(4*A) + B*y^2 + D*y = 0;
 (8)

Now i must  get this form A( )^2 +B( )^2 = M

 >

## What does ``ambiguous use of `^`'' mean?...

Does this condition happen when the character is too long?

## Using toroidal in PDEchangecoords & defining inver...

Hello everybody,

i am trying to use PDEchangecoords to transform a system of differential equations from Cartesian coordinates to toroidal coordinates. However, when i use a user defined coordinate transform from toroidal to Cartesian, i don't get the initial equations. Please find attached a minimal working environment.

i would highly appreciate your hints and suggestions!

Thank you

Best regards,

F

 (1)

## How to inverse interpolate a 2D lookup table in Ma...

Dear Community,

I would like to have an inverse interpolation with a 2D lookup table in MapleSim. The usual 2D lookup interpolation has u1 column values, and u2 row values, and a corresponding   y   table values, i.e. y = f(u1,u2). Now I would like to go the reverse way. Suppose I know y, and u2, and I would like to get u1. How can I implement this in MapleSim? An additional information is, that the 3D surface represented by the f(u1, u2) function is a smooth, slightly curved, monotonically sloping surface, so to any  y  value a unique pair of u1 and u2 values belong.

With my specific data, which are attached in the TestVLP.xlsx file:

• u2 values are: 1st row, cells 2 .. 14
• u1 values are  1st column, rows 2 .. 11
• tabulated values are all the rest, i.e. from cell(2,2) .. cell(11,14)

Now for my case:

• u2 = 42000.0
• y   = 94.5614

How much is u1? I know the correct answer from elsewhere, it should be something very close to u1 ~ 85. This  y  value is in the rectangle bordered by columns 7 .. 8  and rows 5 .. 6 in the Excel file.

So my question is how do I correctly implement this in MapleSim? As visible from the attached TestInverse2DInterpolation.msim file I tried to do it with an Inverse Block Constraints component and a horizontally flipped 2D Lookup Table (VLP) and Constants for y and u2, but upon running MapleSim I get an error message that no solution is found, although the solution is relatively easy and straightforward. May I ask you to have a look at it, what can be the problem here, what do I do wrong? I’m using MapleSim 2019.2.

best regards

Andras

TestInverse2DInterpolation.msim

TestVLP.xlsx

## Euler-Bernoulli Beam using Krylov–Duncan Method...

Hello Everyone!

I have one more challenge for you.

How can I find for a Free-Pinned-Pinned-Free (3-span) beam (Picture A below) using the Krylov–Duncan Method (Literature links and references below):

- the matrix of the system?

- the transcendental equation in order to determine the natural frequencies?

- the first three mode shapes?

I tried to do it as you can see from my MAPLE (file below), but I got stuck when I use the command "determinant" and it did not find the transcendental equation.

Krylov_function_free_pinned_pinned_free_beam.mw

Picture_A

References:

Krylov–Duncan Method