Surprisingly, Maple can get the symbolic solution to this very quickly if you give it just a tiny bit of help. It is trivial to solve ode1 for V(t) and substitute that into ode2. Then dsolve solves it in a few seconds. 

Download moji_solved.mw

This is not a problem with LinearAlgebra:-Equal.

When a Matrix (or other rtable) contains a symbolic (the a in your case) and that symbolic is changed, the Matrix is not automatically updated. One can force the update with rtable_eval:

A := Matrix([[a, 0], [0, 0]]);
for a from 0 to 10 do
     A1:= rtable_eval(A);
     if LinearAlgebra:-Equal(A1^2, A1) then print(a, A1) end if
end do;

I consider it a bad programming practice to use a for loop's index variable as a symbolic. However, Maple does allow it. So I'd rewrite the code as

A:= < < a, 0 > | < 0, 0 > >:
for k from 0 to 10 do
     A1:= eval(A, a= k);
     if LinearAlgebra:-Equal(A1^2, A1) then print(k, A1) end if
end do: 

Why the method labelled "PROCEDURE" isn't working for you:

(I think that you already figured this out on your own.)

In this method, you've just moved the global/parameter conflict to an earlier procedure. In your procedure named qpercentagedifference, the parameter height is not the same as the global height that is "in" the variables qtotal and qpresent. Note that expressions created with the arrow (->) and with proc are essentially the same to Maple--they are both considered procedures.

In order to use this method, you have to be consistent "down through the chain" and make every expression using height a procedure with height as a parameter.

Why the method labelled "SUBS" isn't working for you:

The subs does not change the expression being substituted; rather it creates a new expression. For example, subs(x= _x, y) does not change y. There are several things that you can do to fix this.

(1)
modalmasspedestriansfail:= proc(subsheight)
     if subs(height= subsheight, qpercentagedifference) >= 5/100 then
          subs(height= subsheight, modalmasswithpedestrians)
     else
          subs(height= subsheight, modalmasswithoutpedestrians)
     end if
end proc:

(2)modalmasspedestriansfail:= proc(subsheight)
     local A, B, C;
     A,B,C:= subs(
          height= subsheight,
          [qpercentagedifference,
           modalmasswithpedestrians,
           modalmasswithoutpedestrians
          ]
    )[];
     if A >= 5/100 then B else C end if
end proc

(3)
modalmasspedestriansfail:= proc(subsheight)
     subs(
          height= subsheight,
            `if`(
                  qpercentagedifference >= 5/100,
              modalmasswithpedestrians,
                  modalmasswithoutpedestrians
             )
     )
end proc:

The problem has nothing to do with the if...then. In both of your examples, there are two different variables named height, one a global and one a procedure parameter. In your first example--the one the doesn't work--you are trying to use the global as the parameter. Here's a simplified version of your first example:

y:= x^2:
f:= proc(x) y end proc:

The x that is "in" y is not the same as the parameter x. This procedure won't plot.

There are several ways around this problem. One way is to make y a procedure:

y:= x-> x^2:
f:= proc(x) y(x) end proc:

A second way is to use a different name and subs one for the other:

y:= x^2:
f:= proc(_x) subs(x= _x, y) end proc:

A third way is unapply:

y:= x^2:
Y:= unapply(y, x):
f:= proc(x) Y(x) end proc:

And there are several more ways.

In your second example, the one that works, the height appears explicitly in the procedure. But, as you probably realize, this is not a good way to do it because you had to copy the expression into the procedure. Copying sections of code is always undesirable.

It looks like Maple ran out of memory trying to solve your equation symbolically. Get a numeric solution instead.

You can plot the solutions with plots:-odeplot. See ?dsolve,numeric and ?plots,odeplot .

Example: Plot t vs. L(t):

plots:-odeplot(Sol, [[t,L(t)]], t= 0..100)

For some reason I can't compile on my computer. (And I'd appeciate some advice on how to correct that.)

Anyway, Acer's evalhf code runs in 2.55 secs on my computer. By parallelizing that and making some small tweaks to the innermost loop (removing the extra trunc), I got that down to 0.815 secs (modulo my eight processors). The parallelization should also work with the compiled version, but I can't test that. (But I left in the code for the compiled version, of course.) Here's the code: Simu_para_evalhf.mw

Like this:

BVP:= {diff(y(x),x$2)-2*y(x)=0,y(0)=1.2,y(1)=0.9}:
Sol_num:= dsolve(BVP, numeric, method=bvp[midrich], output= listprocedure):
Sol_exact:= dsolve(BVP):
Res:= eval(y(x), Sol_num) - unapply(eval(y(x), Sol_exact), x):
plot(Res, 0..1);

The remaining time can be cut in half (!!!) simply by replacing frac(x) with x - trunc(x) since trunc(x) has already been computed. frac is symbolic, and trunc is kernel. It's amazing how much of a difference this makes.

Like most code that generates a lot of random numbers, this one is an obvious candidate for parallelization. It just required a trivial change to your outermost procedure and converting writable globals to locals (which is good coding practice anyway). The benefit that you derive from this will be proportional to the number of processors that you have. I have eight, most modern home computers have four. Windows Resource Monitor showed that I had 100% utilization on all processors, so parallelization can't get any better than that.

Making these two changes, I got the time down to 6 seconds. Here is the modified code: Simulation_Para.mw

There should be no loop for i from 1 to Size in procedure SampleQ. The loop in Qsim is already for i from 1 to Size. So SampleQ should begin

SampleQ:=proc()
    global Q,obs,forv,A,rSum,cSum;
    local number,i,j,k,n,m,broekdel;    
   
     obs:=Matrix(r,c):   #Creating a r times c matrix with zeroes - to hold the observed values
     forv:=Matrix(r,c):   #Creating a r times c matrix with zeroes - to hold the expected values
     A:=Sample(X,1..Total):   

...

This reduces the run time to 51 seconds for me.

Since I think that you're using a less-than-most-recent version of Maple, see ?grelgroup . If you've upgraded to Maple 17 since we've last talked about it, then see ?GroupTheory,Group . In either case, "words" are represented as lists; so instead of a*b*a^(-1), you'd use [a,b,a^(-1)] or [a,b,1/a].

To represent the group that you used in your example:

G:= grelgroup({a,b}, {[a,a], [b,b], [a,b,1/a,1/b]});

(You can use a^(-1) instead of 1/a if you prefer.)

In this representation, a and b are called the generators.

G is a group, but not a permutation group because its elements are not permutations (a is just a letter, obviously; so it's not a permutation). However, every group is isomorphic to some permutation group. G has four elements: [e, a, b, ab] (where e is the identity element). Make that list correspond to [1,2,3,4]. Now we wish to find the permutation that corresponds to a. Multiply each element of the list by a (this group is abelian (commutative), so order doesn't matter) and you get [ae, aa, ab, aab] = [a, e, ab, b], which corresponds to [2,1,4,3], which is [[1,2],[3,4]] in disjcyc notation. So, in a sense of "is", a "is" the permutation [[1,2],[3,4]], but only because of the order that we listed the elements. Likewise, if we multiply the original list by b, we find that b corresponds to the permutation [[1,3], [2,4]]. Those two elements are enough to generate the group. We can now say

GP:= permgroup(4, {a= [[1,2],[3,4]], b=[[1,3],[2,4]]});

Now, it turns out that this is the minimal-degree permutation representation of this particular group, but that was just luck. The technique outlined here will always give a representation of degree the same as the order of the group, but there is usually a representation of lesser degree.

I hope that that increased your understanding and didn't cause more confusion.

Another way:

[seq](lambda - x^2, x= r);

The  way that looks closest to the original is

lambda -~ r^~2;

I believe these elementwise operators have been available since Maple 13.
 

What you call a "permutation matrix" is not a permutation matrix. Quoting directly from the first sentence of the Wikipedia article "Permutation Matrix"

a permutation matrix is a square binary matrix that has exactly one entry 1 in each row and each column and 0s elsewhere.

The randomize() command should only be used once per session (once per restart). If it is executed twice in rapid succession, it can choose the same seed, since the seed is based on the clock, and Maple's clock is very coarse-grained for today's computers. Here's an example showing how long it can take for that clock to tick:

R:= proc() randomize(); rand() end proc:
X:= R():
for k while X=R() do end do:
X:= R():
for k while X=R() do end do:
k;
                             73112

You say that you need a different seed for each trial? Why? You can set the seed by passing an argument to randomize:

randomize(1);
randomize(2);

etc. Each will generate a different series of random numbers. But if you don't do the subsequent randomizes, you're going to get different random numbers anyway.

Disjoint cycle notation does not represent fixed points, so there are no singletons in that notation.

The command mulperms is for multiplying permutations. Your f and g are not permutations; they are groups of permutations.

fgen:= convert([3,2,4,1], disjcyc);
                          [[1, 3, 4]]
ggen:= convert([2,4,3,1], disjcyc);
                          [[1, 2, 4]]
f:= permgroup(4, {fgen}):
g:= permgroup(4, {ggen}):
group:-mulperms(fgen, ggen);
                        [[1, 3], [2, 4]]
f1:= group:-RandElement(f);
                          [[1, 3, 4]]
g1:= group:-RandElement(g);
                          [[1, 4, 2]]
group:-mulperms(f1,g1);
                          [[1, 3, 2]]

The interface commands will only affect displays made after you change the setting; it will not affect what is already on the screen. This is also true if you change the settings from the Tools -> Options menu and select Apply to Session.

If you want to see more of the internal structure of Maple objects, a good command to use is lprint.