Carl Love

Carl Love

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13 years, 162 days
Himself
Wayland, Massachusetts, United States
My name was formerly Carl Devore.

MaplePrimes Activity


These are replies submitted by Carl Love

@abbeykabir The algorithms are not in packages. They are all accessible via the method option: dsolve(..., numeric, method= ...). They are documented on the help pages ?dsolve,numeric,IVP , ?dsolve,numeric,BVP , and ?dsolve,numeric,classical .

@abbeykabir The algorithms are not in packages. They are all accessible via the method option: dsolve(..., numeric, method= ...). They are documented on the help pages ?dsolve,numeric,IVP , ?dsolve,numeric,BVP , and ?dsolve,numeric,classical .

Under the rules, why is p(2014) = 30? Shouldn't it be 8?

@Markiyan Hirnyk I didn't feel like looking at or printing out a long number. Also, it's nice to be able to assign the answer to a variable.

@Markiyan Hirnyk I didn't feel like looking at or printing out a long number. Also, it's nice to be able to assign the answer to a variable.

@Vladimir K. Here it is. But there is nothing "wrong" in M14. As Markiyan suggests, such results are to be expected when you use simplify(..., symbolic).


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restart:

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Za:=simplify(int(((c-x)/x)^n,x=a..c),symbolic) assuming a>0,c>a,n>-1;

(Pi*n^2*c+c^n*a^(-n+1)*hypergeom([-n, -n+1], [2-n], a/c)*sin(n*Pi)-Pi*n*c)/((n-1)*sin(n*Pi))

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Zb:=simplify(int(((x-c)/x)^n,x=c..b),symbolic) assuming c>0,b>c,n>-1;

-(1/2)*(n^2*c^2*hypergeom([1, 1, 2-n], [2, 3], c/b)*sin(n*Pi)+2*cos(n*Pi)*Pi*b*c*n-2*sin(n*Pi)*gamma*b*c*n+2*sin(n*Pi)*ln(b)*b*c*n-2*sin(n*Pi)*ln(c)*b*c*n-2*sin(n*Pi)*Psi(-n+1)*b*c*n-n*c^2*hypergeom([1, 1, 2-n], [2, 3], c/b)*sin(n*Pi)+2*sin(n*Pi)*n*c*b-2*sin(n*Pi)*b^2)/(b*sin(n*Pi))

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Z2:=(A,B,C)->subs(a=A,c=C,Za)-subs(b=B,c=C,Zb);

proc (A, B, C) options operator, arrow; subs(a = A, c = C, Za)-subs(b = B, c = C, Zb) end proc

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INT:=simplify(Z2(A,B,(A+B)/2)) assuming A>0,B>0,C>0,C>A,B>C,n>0;

(1/8)*(-4*B^2*hypergeom([-n, -n], [-n+1], 2*A/(A+B))*A^(-n+1)*sin(n*Pi)*2^(-n)*(A+B)^n-4*A^(2-n)*B*hypergeom([-n, -n], [-n+1], 2*A/(A+B))*sin(n*Pi)*2^(-n)*(A+B)^n+4*B^2*A^(-n+1)*sin(n*Pi)*(-2/(A-B))^(-n)-4*A^(2-n)*B*sin(n*Pi)*(-(1/2)*A+(1/2)*B)^n+A^3*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2-A^3*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A^2*B*Pi*n+4*A^2*B*sin(n*Pi)*n+4*A*B^2*Pi*n+4*A*B^2*sin(n*Pi)*n+4*A*B^2*sin(n*Pi)*n*ln(2)-4*A^2*B*sin(n*Pi)*n*ln(A+B)+4*A^2*B*sin(n*Pi)*n*ln(2)-4*A*B^2*sin(n*Pi)*n*ln(A+B)+2*A^2*B*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2+A*B^2*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2-4*A^2*B*gamma*sin(n*Pi)*n+4*A^2*B*Pi*cos(n*Pi)*n-4*A^2*B*Psi(-n+1)*sin(n*Pi)*n-2*A^2*B*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A^2*B*sin(n*Pi)*ln(B)*n-4*A*B^2*gamma*sin(n*Pi)*n+4*A*B^2*Pi*cos(n*Pi)*n-4*A*B^2*Psi(-n+1)*sin(n*Pi)*n-A*B^2*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A*B^2*sin(n*Pi)*ln(B)*n-8*A*B^2*sin(n*Pi))/(B*sin(n*Pi)*A)

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RI:=simplify(evalc(Re(INT))) assuming A>0,B>0,C>0,C>A,B>C,n>0;

(1/8)*(-4*B^2*hypergeom([-n, -n], [-n+1], 2*A/(A+B))*A^(-n+1)*sin(n*Pi)*2^(-n)*(A+B)^n-4*A^(2-n)*B*hypergeom([-n, -n], [-n+1], 2*A/(A+B))*sin(n*Pi)*2^(-n)*(A+B)^n+4*B^2*A^(-n+1)*sin(n*Pi)*(-2/(A-B))^(-n)-4*A^(2-n)*B*sin(n*Pi)*(-(1/2)*A+(1/2)*B)^n+A^3*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2-A^3*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A^2*B*Pi*n+4*A^2*B*sin(n*Pi)*n+4*A*B^2*Pi*n+4*A*B^2*sin(n*Pi)*n+4*A*B^2*sin(n*Pi)*n*ln(2)-4*A^2*B*sin(n*Pi)*n*ln(A+B)+4*A^2*B*sin(n*Pi)*n*ln(2)-4*A*B^2*sin(n*Pi)*n*ln(A+B)+2*A^2*B*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2+A*B^2*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n^2-4*A^2*B*gamma*sin(n*Pi)*n+4*A^2*B*Pi*cos(n*Pi)*n-4*A^2*B*Psi(-n+1)*sin(n*Pi)*n-2*A^2*B*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A^2*B*sin(n*Pi)*ln(B)*n-4*A*B^2*gamma*sin(n*Pi)*n+4*A*B^2*Pi*cos(n*Pi)*n-4*A*B^2*Psi(-n+1)*sin(n*Pi)*n-A*B^2*hypergeom([1, 1, 2-n], [2, 3], (1/2)*(A+B)/B)*sin(n*Pi)*n+4*A*B^2*sin(n*Pi)*ln(B)*n-8*A*B^2*sin(n*Pi))/(B*sin(n*Pi)*A)

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II:=simplify(evalc(Im(INT))) assuming A>0,B>0,C>0,C>A,B>C,n>0;

0

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Download symbolic.mw

@abbeykabir Dividing by a matrix is equivalent to multiplying by its inverse. Let J(x) represent the Jacobian matrix evaluated at the vector x. Then the Newton iteration becomes

x[i+1]:= x[i] - J(x[1])^(-1)*F(x[i]).

But recall what I called The first rule of numerical linear algebra: Never invert a matrix; always solve a linear system instead. Computing A^(-1)*B is equivalent to solving A*X=B. This is accomplished in Maple with the command LinearAlgebra:-LinearSolve(A,B).

Now let's step back for a moment to the single-variable Newton iteration:

x[i+1]:= x[i] - f(x[i])/f'(x[i]).

How do we know when to stop iterating?

@abbeykabir Dividing by a matrix is equivalent to multiplying by its inverse. Let J(x) represent the Jacobian matrix evaluated at the vector x. Then the Newton iteration becomes

x[i+1]:= x[i] - J(x[1])^(-1)*F(x[i]).

But recall what I called The first rule of numerical linear algebra: Never invert a matrix; always solve a linear system instead. Computing A^(-1)*B is equivalent to solving A*X=B. This is accomplished in Maple with the command LinearAlgebra:-LinearSolve(A,B).

Now let's step back for a moment to the single-variable Newton iteration:

x[i+1]:= x[i] - f(x[i])/f'(x[i]).

How do we know when to stop iterating?

Are the entries rational functions? How many parameters? Are you looking for a particular eigenvalue?

Try LinearAlgebra:-CharacteristicPolynomial.

Try setting one parameter to 0 or 1.

 

@mvcr15 Wikipedia has good information. Let's start with Euler's method for a single equation. That's the easiest case. You should be able to find a discussion of it in any serious calculus textbook. Or see the Wikipedia article "Euler method".

@abbeykabir Okay, good. Yes, the Jacobian matrix is the derivative of a multivariate function. The single-variable Newton's method divides by the derivative. In the multivariate case the derivative is a matrix. How can we divide by a matrix?

@abbeykabir Okay, good. Yes, the Jacobian matrix is the derivative of a multivariate function. The single-variable Newton's method divides by the derivative. In the multivariate case the derivative is a matrix. How can we divide by a matrix?

Do you need the methods to solve a single first-order differential equation, or do you need it for a system of equations?

@abbeykabir Ok, that's good. Now let's generalize that to the multivariate case, where x is an n-vector, and f is a vector-valued function on n-vectors (i.e., f: R^n -> R^n). In particluar, what corresponds to the derivative in the multivariable case?

@abbeykabir Ok, that's good. Now let's generalize that to the multivariate case, where x is an n-vector, and f is a vector-valued function on n-vectors (i.e., f: R^n -> R^n). In particluar, what corresponds to the derivative in the multivariable case?

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