Hello all,

I'm experiencing an aggravating issue when substituting numerical values into a symbolic expression.  I'm using Maple 14.  I believe the issue may be related to floating point precision.  Either way, it's ruining my life.  If anyone has a solution or a work-around, I'd be most grateful.  The following code reproducibly produces the anomolay on my machine:

vx := Vector( 4, symbol=x ):

# A numerator and a denominator. They're equal.
num := (x[1]*x[3]+x[1]*x[4]+x[2]*x[3]+x[2]*x[4])^2:
den := ((x[1]+x[2])^2*(x[3]+x[4])^2):

# Prints true...
evalb(num=den);

# This equals zero
y := 0.1 - 0.1*num/den;

# Prints 0...
simplify(y);

# Prints 0...
simplify(subs(x[3]=1,x[4]=3,0.1-0.1*num/den));

# Prints 0...
simplify(subs(x[3]=1,x[4]=3,y));

# Prints 0.1 x 10^-10 !?!?
simplify(subs(x[3]=1,x[4]=2,y));

Hello,

I have a little problem. I have a system of ODEs, I can solve (with numeric solve) it but I can't plot it...
Any idea to help ?

Thank you !!

Here is my code:

with(DEtools);
beta := 1; lambda := 5; nu := 1; Delta := 1;


sys := {C(0) = 0, In(0) = .2, diff(C(u), u) = beta*In(u)*s(u)-C(u)/nu, diff(In(u), u) = C(u)/nu-In(u)/lambda+Delta*(diff(diff(In(u), u), u)), diff(s(u), u) = -beta*In(u)*s(u), s(0) = .8, (D(In))(0) = .2}

dsys := dsolve(sys, numeric, [In(u), s(u), C(u)])

plot(dsys[1], u = 0 .. .5, axes = boxed)

And I have this error:

Warning, expecting only range variable u in expression dsys[1] to be plotted but found name dsys[1]


PS: Maple solves the system without any problem:

 dsys(.5);

        [                                              
        [u = 0.5, In(u) = HFloat(0.33305297276372425),
        [                                              

           d                                       
          --- In(u) = HFloat(0.33950703755414946),
           du                                      

          s(u) = HFloat(0.7022184797811994),

                                           ]
          C(u) = HFloat(0.0781621551198558)]
                                           ]

Hi!

I use 'alias' to define variable dependencies.
But when I want to use the result of my calculation as an expression, I bite the dust; I cannot get rid of the dependencies.
Can anyone help me here?

In the simplified example below, I use the independent variables z[3] and z[4] to define z[1](z[3],z[4]) and z[2](z[3],z[4]).
I then introduce a function f[1](z[3],z[4]) and its derivatives df_dz.
I introduce the names dz[1]/dz[3]=Dp[1,3], dz[1]/dz[4]=Dp[1,4] etc...
When I have calculated df_dz[3], however, I cannot insert values of z[2] without affecting Dp[2,3].
Actually, now I have finished my calculation and want df_dz[2,3] to be a regular expression, so that I can insert values of
z without affecting the Dp:s.
How can I convert df_dz[3] to a regular expression?

alias( seq(z[i]=z[i](seq(z[j],j=3..4)),i=1..2)):
alias(f=f(seq(z[j],j=3..4))):
alias(seq(seq(Dp[m,n]=diff(z[m](seq(z[j],j=3..4)),z[n]),m=1..2),n=3..4)):

f:=z[1]-z[2]*z[3]:

for j from 3 to 4 do
df_dz[j]:=diff(f,z[j]);
od:

df_dz[3];
subs(z[2]=4711,df_dz[3]);
whattype(Dp[1,3]);
whattype(z[3]);




function

indexed

Hi there,

I'm relativly new to maple and right now I'm trying to plot a couple of points (as part of a TSP-Solution) by doing the following:

with(plots):

p := [[565,575],[685,595],[700,580],[770,610]];

pointplot(p, connect=true);

Unfortunately it doesn't number the points. What I'm trying to do is that the above four points have a number or an index so I can see which point is where. 

Is there a way to do this?

thanks

restart:

Eq1:=x=(phi*(theta[m]-1/x)/theta[m]+(1-phi)/2);

solve({Eq1},x);

x := (1/4)*(phi*theta[m]+theta[m]+sqrt(phi^2*theta[m]^2+2*phi*theta[m]^2-16*phi*theta[m]+theta[m]^2))/theta[m];

Now plotting the first root

p1:=plot(subs(phi=0,x),theta[m]=0..14,color=red):
p2:=plot(subs(phi=0.1,x),theta[m]=0..14,color=green,linestyle=2):
p3:=plot(subs(phi=0.5,x),theta[m]=0..14,color=blue,linestyle=3):
p4:=plot(subs(phi=1,x),theta[m]=0..14,color=black):
display({p1,p2,p3,p4},axes=boxed,view=[0..14,0..1]);

Note: I'm unable to reproduce the following plot. Any idea?

 SA.mw

I'm a student. I want to purchase oline Maple Student, but I can't.

Please send me a feedback as soon as possible. Thanks.

I am attempting to plot an initial value problem in Maple 18.  I have my equation defined, as well as a general solution and two particular solutions at y(0)=3/4 and y(0)=1/2.  To graph, I entered the command

DEplot(de,y(x),x=-3..3,{[0,1/2],[0,3/4]},dirgrid=[12,12],color=black,linecolor=blue,thickness=2);

but instead of returning a graph, the software gave me the error message

Error, (in DEtools/DEplot/CheckDE) extra unknowns found: sinx

The Maple support site lists this as an unknown error, and as a new user, I'm not sure what to do.  What does this mean?

Hi everyone,

I've been having a problem trying to correct this procedure so that it will accept empty tables as well. This is the code I've been messing up with:

6.10.mw

If someone could help me with this, it would be really appreciated.

Hi,

So I have a simple while loop and keep receiving this error and have no idea how to fix it. I don't get why it works for the first few, and then the error starts. Here is my code and output:

Input:

restart;
n:=0:
x:=Pi/3;
m:=0:
total:=0:
while abs(1/2-total) > 10^(-8) do
k:=((-1)^(n/(2))*x^(n))/(n!):
total:= total +k;
evalf(total, 11);
print(%);
n:=+2;
end do:

OUTPUT:
1
- Pi
3
1.
0.45168864437
Error, cannot determine if this expression is true or false: 0 < -50000001/100000000+(1/18)*Pi^2

Why does it think i'm asking if something is greater than 0? Any help??

I wish to convert:

Sum(x[k],k=1..n)*Sum(y[k],k=1..m) -> Sum(Sum(x[j]*y[k],j=1..n),k=1..m)

Can anybody show me an elegant way to do it?

Gracias

Hello:

I have a simple program to find the intercepts of an equation but I would like to program to ask the user:Would you like the run the program again?  Below is my code:

interceptslope()

all the program stuff

end proc:

Do you want to run the program again? Yes/No

How do I call the program again

Lonnie

Good day everyone, how can one check for the congence of numerical solution of this ODE in maple? See it here 1.mw

Best regards.

Can the spacing between gridlines on a plot be modified? i.e., can I have more lines?

I've got the following 

with(plots):
tubeplot([cos(t),sin(t),t], t=0..6*Pi, radius=1/3,
style=patchnogrid, shading=Z, axes=box, orientation=[40,70]);

which gives the plot of a spiral and need to make an animation of a rotating spiral.

I've tried 

animate([cos(t),sin(t),t], t=0..6*Pi,numpoints=200,frames=20,shading=Z,axes=box) but that doesn't work. What am I doing incorrectly?

Hi, Very new to Maple. This is a math assignment, and well I am not exactly sure what is happening. I have had a buddy to help me, but things are not necessarily working. Using Maple17.
This is what I have so far.

de := sin(x)*(diff(y(x), x))+cos(x)*y(x) = Q;
/ d \
sin(x) |--- y(x)| + cos(x) y(x) = Q
\ dx /
dsolve(de);
Q x + _C1
y(x) = ---------
sin(x)
ab := 75; Q := 2-0.1e-1*ab; M := 4+0.1e-1*ab;
75
1.25
4.75
PS := simplify(dsolve({de, y((1/2)*Pi) = M}, y(x)));
-10 x - 38 + 5 Pi
y(x) = - -----------------
8 sin(x)
z := rhs(PS);
-10 x - 38 + 5 Pi
- -----------------
8 sin(x)
N := evalf(subs(x = .4, z));
8.439521805
a := z, x = 0 .. Pi, y = 0 .. 10; b := plots[pointplot]([(1/2)*Pi, M]); c := plots[pointplot]([.4, N]); d := plots[pointplot]([x0, y0]); plots[display]({a, b, c, d});
z, x = 0 .. Pi, y = 0 .. 10
Error, (in plots:-pointplot) points cannot be converted to floating-point values
Error, (in plots:-pointplot) points cannot be converted to floating-point values
Error, (in plots:-pointplot) points cannot be converted to floating-point values
Error, (in plots:-display) expecting plot structures but received: {c, d, z, plots:-pointplot, x = 0 .. Pi, y = 0 .. 10}