Markiyan Hirnyk

Markiyan Hirnyk
10 years, 166 days


These are questions asked by Markiyan Hirnyk

Let us consider the maximum value of the polynomial

x^4+c*x^2+x^3+d*x-c-1

on the interval x=-1..1 as a function g of the parameters c and d. General considerations suggest its continuity. However, a plot3d of g does not  confirm it.  Also the question arises "Is the function g(c,d) bounded from below?". Here is my try with the DirectSearch and NLPSolve:

 

restart;
``

g(10, -10)

9.

(1)

plot(x^4+x^3+10*x^2-10*x-10-1, x = -1 .. 1)

 

plot3d(g, -5 .. 5, -5 .. 5, grid = [100, 100], style = surface, color = "DarkOliveGreen")

 

DirectSearch:-GlobalOptima(proc (a, b) options operator, arrow; g(a, b) end proc, {a = -1000 .. 1000, b = -1000 .. 1000}, variables = [a, b])

[-167.208333252089, Vector(2, {(1) = 999.9999999975528, (2) = 166.20833325208952}, datatype = float[8]), 815]

(2)

DirectSearch:-GlobalOptima( (a, b) -> g(a, b), variables = [a, b])

DirectSearch:-GlobalOptima(proc (a, b) options operator, arrow; g(a, b) end proc, variables = [a, b])

Error, (in Optimization:-NLPSolve) invalid input: PolynomialTools:-CoefficientVector expects its 1st argument, poly, to be of type polynom(anything, x), but received HFloat(HFloat(undefined))*x^4+HFloat(HFloat(undefined))*x^3+HFloat(HFloat(undefined))*x^2+HFloat(HFloat(undefined))*x+HFloat(HFloat(undefined))

 

``

 

Download bound.mw

 

I mean

J := int((x^2+2*x+1+(3*x+1)*sqrt(x+ln(x)))/(x*sqrt(x+ln(x))*(x+sqrt(x+ln(x)))), x);

Of course, with Maple.

How to solve the inequality

,

assuming a::real ?

Of course, with Maple. I'd like to demonstrate the difficulties, solving

>solve(log[2*abs(x-a)](abs(x+a)+abs(x-a)) < 1, x) assuming a > 0, a < 1/2

.

The correct answer under the above restrictions is

{x  > 0, x  <  a} union {a  <  x, x <  a + 1/2} union { -infinity < x, x < a - 1/2}.

This is a problem from Lviv math school olympiad '2016.

 

 

Here is my unsuccessful try

>restart; plots:-contourplot(exp(2*x/(x^2+y^2)), x = -2 .. 2, y = -2 .. 2,
grid = [100, 100], coloring = [blue, red], contours = [.1, .3, .5, 1, 2]);

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