## 1401 Reputation

7 years, 165 days

 (1)

 (2)

 (3)

 (4)

 (5)

## Another way....

```restart;
with(LinearAlgebra);
w := (2*Pi)/14;
v := Vector([1, sin(w*t), cos(w*t)]);
simplify(eval(sum(v . (Transpose(v)), t = k .. k + n), n = 13));```

## Try:...

```restart;
ODE := diff(W(x), x \$ 2) + (A*ohm^2*ro - kd)*W(x)/T = p;
sol1 := dsolve(ODE, W(x));
assign(sol1);

subs(_C1 = 0, W(x));

#or:

eval(W(x), _C1 = 0);

#sin(sqrt(A*ohm^2*ro - kd)*x/sqrt(T))*_C2 + p*T/(A*ohm^2*ro - kd)
```

## Another way:...

```int(exp(-2*r)*cos(theta)^3*r^2*sin(theta), phi = 0 .. 2*Pi, r = 0 .. infinity, theta = 0 .. Pi);
#O
```

## Series solution....

We can find solution with series representation:

```restart;
odeSystem := {diff(y1(x), x) = -x*y2(x) - (1 + x)*y3(x), diff(y2(x), x) = -x*y1(x) - (1 + x)*y4(x), diff(y3(x), x) = -x*y1(x) - (1 + x)*y4(x) - 5*x*cos(1/2*x^2), diff(y4(x), x) = -x*y2(x) - (1 + x)*y3(x) + 5*x*sin(1/2*x^2), y1(0) = 5, y2(0) = 1, y3(0) = -1, y4(0) = 0};
Order := 10;
systemSol := dsolve(odeSystem, [y1(x), y2(x), y3(x), y4(x)], series);
F := convert(systemSol, polynom);
plot([rhs(F[1]), rhs(F[2]), rhs(F[3]), rhs(F[4])], x = 0 .. 1, color = [red, blue, green, gold], legend = [y1(x), y2(x), y3(x), y4(x)]);```

## A workaround:...

A workaround with Mathematica:

```f[k_] := Sum[(-1)^i (k - i + 1)^(2 k + 4)/((i!)*((2 k - i + 2)!)), {i,0, k}];
L = Table[f[k], {k, 0, 1000}];
FindSequenceFunction[L, k]

(*1/12 (k + 3 k^2 + 2 k^3)*)```

With Maple:

```restart;
with(gfun):
f := k -> sum((-1)^i*(k - i + 1)^(2*k + 4)/(i!*(2*k - i + 2)!), i = 0 .. k);
l := [seq(f(k), k = 0 .. 1000)];
rec := listtorec(l, u(k), [ogf]);
rsolve(op(1, rec), u(k));

#1/6*k^3 + 3/4*k^2 + 13/12*k + 1/2```

## Workaround....

See attached file.

integral.mw

## Another way....

```Sum((-1)^k*sin(k*x)/k, k = -infinity .. infinity) = evalc(sum((-1)^k*sin(k*x)/k, k = -infinity .. infinity, formal))
```

## One way is:...

```f := x -> convert(sin(theta), x);
map(f, [cos, tan, cot, csc, sec]);```

#[-cos(theta + Pi/2), 2*tan(theta/2)/(1 + tan(theta/2)^2), 2*cot(theta/2)/(cot(theta/2)^2 + 1), 1/csc(theta), -1/sec(theta + Pi/2)]

## Numerically....

```sol := dsolve({diff(f(x), x) = f(1/x), f(0) = 0}, numeric, delaymax = 1.0, delaypts = 2000);
plots:-odeplot(sol, [x, f(x)], x = -1 .. 1);```

Maybe you can try with another initial condition f(0)=1 ?

## Simpler....

```evalf[30](subs(z = 2 + 3*I, Zeta(-z) + 2*z!*sin(Pi*z/2)*Zeta(z + 1)/(2*Pi)^(z + 1)));

rtable([seq(evalf[2^m](subs(z = 2 + 3*I, Zeta(-z) + 2*z!*sin(Pi*z/2)*Zeta(z + 1)/(2*Pi)^(z + 1))), m = 1 .. 10)], subtype = Vector[column]);#Depending of the precise```

## Another sum...

I have another sum with Laguerre polynomials to  give exp(z).

`Sum((m + 1)!*z^k*LaguerreL(k, k + m, z)/(k + m + 1)!, k = 0 .. infinity) = exp(z)`

We can check:

```restart;
f := (z, m) -> sum((m + 1)!*z^k*LaguerreL(k, k + m, z)/(k + m + 1)!, k = 0 .. infinity)
interface(rtablesize = 100);
rtable([seq([m, evalf(f(1, m))], m = 0 .. 20)], subtype = Vector[column]);```

```Digits := 30;
f := (x, m) -> sum(m!*x^(m - n)*LaguerreL(m, n - m, x)^2/n!, n = 0 .. infinity);
interface(rtablesize = 100);
rtable([seq([m, evalf(f(1, m))], m = 0 .. 20)], subtype = Vector[column]);```

## Fracdiff equation in Maple....

From this book on page 152 I borrowed the code.

See attached files.

fracdiff.mw

fracdiff_for_alpha=1_test.mw

For first question:

`Int(exp(-(abs(x - mu)/sigma)^beta), x = -infinity .. s) = piecewise(Or(s = mu, s <= 0), sigma*GAMMA(1 + 1/beta), And(mu < s, 0 < s), ((-s + mu)*Ei(-(1 + beta)/beta, (s - mu)^beta*sigma^(-beta)) + 2*sigma*GAMMA(1/beta))/beta, sigma*GAMMA(1/beta, (-s + mu)^beta*sigma^(-beta))/beta)`

## Try...

Try this:

```eq := 2*exp(-2*t) + 4*t = 127;
solve([eq, 0 < t], {t});
limit(LambertW(-exp(-x))/2 + 127/4, x = infinity);
interface(rtablesize = 100);
rtable([evalf[100](seq(limit(LambertW(-exp(-x))/2 + 127/4, x = m), m = 2 .. 200, 5))], subtype = Vector[column]);```

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