restart;
ddesys := {diff(pred(t), t) = pred(t)*[prey(t)/(prey(t)+10)-2/3], diff(prey(t), t) = prey(t)*[2-(1/20)*prey(t-tau)]-prey(t)*[pred(t)/(prey(t)+10)]-10, pred(0) = 1, prey(0) = 1};
 

dsn := dsolve[eval(ddesys, tau = 0)];
plots[odeplot](dsn, [[t, prey(t), color = red], [t, pred(t), color = blue]], 0 .. 300, legend = [prey, pred], labels = [t, ""]);
Error, (in plots/odeplot) input is not a valid dsolve/numeric solution 

I do not understand what i mistake, please help me regarding this issue, thanks in advance

This is a question out of curiosity only ...

I can easily import a matrix from an Excel spreadsheet / source. Maple then displays matrix dimensions, data type, storage and order ... which is fine. Now - suppose I wished to import the standard matrix in question, with all entries displayed - can this be done?

I am working on a problem in geometry where I have ended up with a system of nonlinear ODEs in F and G where F and G are functions of a coordinate y, and A and B are both real constants.  I have included the worksheet where I am working on the equations.

Ric_Equations.mw
 

 I would like to solve these in as explicit a way as possible by obtaining expressions for F and G and was wondering how best to do this with Maple (it doesn't really matter if the explicit solutions are messy, as I just need to know that they exist and can be written down in some form).  I have tried using the dsolve command directly but I receive the error message which you can see above.

Consider A is an nxn binary matrix where n>1000. Assume that there is an integer k<100 such that the entries of the kth power of A, denoted A^k, are all positive integer numbers.  

My problem is that the computation of A^k takes too times and I want to ask: Is there some techniques in Maple for obtaining the matrix A^k. 

One technique that I am used is based on the boolean semiring with 1+1=1. In fact, I evaluate A^k until I reach the full-1 matrix. But the mentioned technique dose not effect the time of computation. 

For example consider the 1024*1024 binary matrix which is given as an attachment. It takes 2278 seconds to find out the entries of the 20th power of this matrix are all positive integer numbers.

I am used the following version of Maple 15. 
Thanks for any suggestions.

 Matrix.txt

Edition(1): The following command maybe useful. From the next command you can upload the given matrix in your worksheet and test it for my claim.

input := FileTools:-Text:-ReadFile("C:/Users/Desktop/Matrix.txt")

Sam := Sample(('Uniform')(10, 20), 30)

My question has two steps:

STEP 1:  The multiplication  of is defined as follows

if n<>l, then

.

if n=l and m<=s,

Question 1: I wrote a code for calculating the multiplication  of. Is it right?

The code for Step 1  

restart;

multiply:=proc(n,m,l,s) local g,a: 
a:=unapply(doublefactorial(2*j-1)/factorial(j),j):
g:=unapply((a(m-j)*a(j)*a(s-j)/a(m+s-j))*(2*m+2*s-4*j+1)/(2*m+2*s-2*j+1),j):

if n<>l then 0 else
sqrt((2*m+1)*(2*s+1))*2^(K/2-1).add((g(j)/sqrt(m+s-2*j+1/2))*phi[n, m+s-2*j],j=0..m) 
end if
end proc:
 
n:=2:
l:=2:
m:=1:
s:=1:
multiply(n,m,l,s);

when I compared the results which I got and the results which is given in the book as follows, I think it is right.

Step 2:

We know that the outer product matrix is calculated as follows 

We found the elements of the outer product matrix in Step 1. 

Question 2 : I want to write the elements which are derived in step 1 to the outer product matrix in step 2. In here, the outer product matrix is NxN matrix. N=(M+1).2^(K-1) where K, M are any integers.

Hello,

How I can take variation from left-hand side of  5, and reach to right-hand side of  5. After by using integral by part obtained  7?

Thank you

I use Maple 2015, is it possible to animate a standing wave as shown below?

 A working animation can be found on https://oceanservice.noaa.gov/facts/seiche.html

Download dummy_1.mw

I want to write a procedure P such that the input of P is a positive integer number n and the output of P is a random permutation of the numbers {1,2,..,n}. 

I know that there is a command in Maple 2017 such that the command produces the mentioned request (random permutation in the combinatoric package), but I should work with Maple 15 and there is no the random permutation command in Maple 15. 

One of the solutions that I am used is based on the random number and check that if the produced numbers are pairwise distinct or not. The problem of this method  is that for n>128, it takes too time to generate a random permutation of the length n.

Thanks for any suggestions. 

I'm trying to better understand the Black and Scholes model; which is a scalar function on (positive reals)^5.
a maplesoft worksheet defines it as

BS_Price=exp(-r*T)*(-(1/2)*erf((1/4)*sqrt(2)*(sigma^2*T-2*r*T+2*ln(K)-2*ln(S[0]))/(sigma*sqrt(T)))+1/2)

I am trying to understand the parameter vectors (r ,T,K,S[0],sigma) that give the same values of BS_Price - and particularly whether these form curves, closed curves, surfaces or similar.

Right now, I am not sure how to procede.

EDIT
I've just put together  a procedure that evaluates BS at points in R^5 - and i think i can move forward by using the curry or rcurry functions to get a 5d tensor of the values of BS, that i can start to look for patterns within.

BS_Price := proc (InterestRate, StockPrice, StrikePrice, Duration, Volatility) evalf(subs([r = InterestRate, S[0] = StockPrice, K = StrikePrice, T = Duration, sigma = Volatility], exp(-r*T)*(-(1/2)*erf((1/4)*sqrt(2)*(sigma^2*T-2*r*T+2*ln(K)-2*ln(S[0]))/(sigma*sqrt(T)))+1/2))) end proc

could anyone give me advice on doing this?
 

The animation in this worksheet seems realistic but I wonder if the physics which is implemented is correct since there is no explicit mention of rotational energy.

ThrowBola.mw

Dear Community,

I have set up a simple 2D RC network with 1 lookup table current source, and a few probes. The model runs fine. Now I wanted to run it from Maple, and followed carefully a MapleSim tutorial which exlained how to establish the link between Maple and MapleSim. I added a worksheet called RCNetworkMaple.mw and run the A := MapleSim:-LinkModel(): command. Then I wanted to run the simulation with the A := Simulate() ; command, but nothing happened, Maple returned A := Simulate(). What did I wrong? In the tutorial it runs perfectly. (Files attached.)

Tx for the kind help in advance,

best regards

Andras

RCNetwork.msim  RC_Rate_Schedule.xlsx

Hellow, help required to remove the errors

 How to  obtain the pressure drop i am unable to get the output. I am uploading the file  and the equations

help_dp.mw