## Substituting variables for numbers issue...

Substituting variables for numbers doesn't always work in some situations.  For example.

a:=sqrt(6)/6

subs(6=b,a)

## sign doesn't work with square roots...

sign doesn't work with square roots

expr := sqrt(3)*x^2*y^4-2*x*y^5+x

sign(expr)

sign(sqrt(3))

## Discrete Fourier Transform...

Hi,

So I need an example of how the discrete fourier transform works, and I would like to do this using Maple but I can't figure out how to plot a discrete function. I have attached an example from wikipedia which is what I would like. It is the function on the right of the image. I have tried plotting a vector but then I can't seem to plot this. Let me know if the question isn't quite clear.

Thanks

## height of the parallepiped with base face describe...

P1 : x + 2y - z = 1

P2 : 2x + 4y - z = 0

formula is s = |d1-d2|/||n||

d1 = 1 d2 = 0 i assume , n = (1 + 2 -1) (P1 pretty much)

So I end up getting 1/(1+4+(-1))²

1/ 6 , and its the correct answer

but I can't figure out how to do this properly in maple, does anyone here know how to? (not sure if i even used the formula correctly to get the correct answer by hand)

sorry for a poorly written question I am in a  rush.

## Doesn't simplify ...

Hi

When i try to simplify this, maple doesn't simplify to the final step.

I hope anyone can help me.

Laura

## How do I replace this variable with a number?...

I want ot replace the free variable introduced by the BackwardsSubstitution procedure with a number. But though the variable looks like x1 I think it must be something else.

problem.maple

## how to generate a binomial sample ...

here my code . iam trying to generate a binomial sample but there is some error occure please help

 >

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 (1)
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 (2)
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 (3)
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## MENTAL BLOCK: Integration conflict...

This should be a simple problem, but I am having trouble resolving a contradiction in integral evaluation that is included in the results below.  Instead of butting my head further perhaps someone can point out my probable error.

You will see in both cases I have a triangle signal with a slope of (-1).  However in the 2nd case I have linked the period T to the slope parameter alpha.  If I assign alpha=1 then the results of the 2 integrals should = 1/4, but the 2nd one does not.

Appreciate any feedback.

 (1)

n=0 term:

 (2)

## How to fix the mantissa ...

Hi,

This is my first question here!

I want to show weird things that can happen in numerical analysis. The example I use is the sum from i=1 to infinity of (1/i) (the harmonic series). In theory this series diverge but in practice it could converge.

I would want all the calculations to use floating point arithmetic with small mantissa (for instance m=1,2,3)). But the problem is I don't know how to fix mantissa in maple... I have the following fonction:

g := n -> evalf[m](sum(evalf[m](1/i),i=1..m))

but evalf just show significant digit without changing the mantissa....

I hope my question is clear! Thanks for your help!

## Error, reserved word `for` unexpected...

Hi, I a have a question, if you can help me I would be pleased

Here is a problem:

for i from 1 to 4 do
if A[i,i]=0 then break
else
for l from i to 4 do
A[i,l]=A[i,l]/A[i,i]:
b[i,1]=b[i,1]/A[i,i]
od:
for j from i+1 to 4
for k from i to 4 do
A[j,k]=A[j,k]-A[j,i]*A[i,k]
od:
b[j,1]=b[j,1]-A[j,i]*b[i,1]
od:
fi:
od:

I definited matrix A and b, but this for loop doesn't work.

## How can I get deleted file back from maple cloud?...

I worked on a document about 2 hours ago. And now when I try to open it, it is empty. I saved it in MapleCloud, and I have had it saved before. So today I opnened the saved file from MapleCloud, but now it is gone. How can I get it back!!? It happend to two of my most important files..

## Bug in Physics metric?...

Hi all,

I found some strange behavior while usings tensors from Physics; I wanted to make sure I wasn't missing something here.

It seems that changing the metric (for instance, to +++-) causes raising and lowering problems. As an example:

```with(Physics):
Setup(metric=`+++-`):

# Define our system of equations
Coordinates(X):

# Define tensors
{U[~mu] = [u(X),0,0,1],
A[~mu]=[0,0,0,n(X)]}:
Define(op(%)):

F[mu,nu]=d_[mu](A[nu]) - d_[nu](A[mu]):
Define(%):

# Multiply tensors
TensorArray(F[~0,~mu].U[mu]);

```

This produces

`-diff(n(X),x1)*u(X)-2*diff(n(X),x4)`

However, only the first term should be present. It seems that changing the mulitplication to F[0,~mu].U[mu] produces the correct output, as does removing the Setup call. Also, manually defining F produces the expected output; only defining it via A seems to generate the discrepancy.

Any idea if this is a bug or a feature?

Thanks!

## How do I include a worksgheet in a question...

I have a worksheet that illustrates a problem I have, How do I make this worksheet available on Mapleprimes?

## How i can get get exact solution to given pde...

PDE := diff(u(x, y), x, x)+diff(u(x, y), y, y)-6*x*y*(1-y)-2*x^3 = 0; BCsx := u(xL, y) = 0, u(xU, y) = y*(1-y); BCsy := u(x, yL) = 0, u(x, yU) = 0; solPDE := pdsolve({BCsx, BCsy, PDE}, u(x, y)); exactSol := unapply(rhs(%), x, y)