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Does Mathematica support in Maximize function to put some variables belong to Integers and others to Reals I tried that but I have an error that this not implemented yet is there any way to do that inside the maximize Function??

I Tried a simple Code to Clarify my question that is

Maximize[{x + y + z, x <= 10, y <= 12.5, 
  z <= 100}, {{x, z} ∈ Integers, {y} ∈ Reals}]

it is ok and gives the output

{122.5, {x -> 10, z -> 100, y -> 12.5}}

I tried in my original problem which is long and tried the same syntax as follows

{{W, H, x1, y1, x2, y2, x3, y3, x4, y4} ∈ 
  Reals, {x12, y12, x13, y13, x14, y14, x23, y23, x24, y24, x34, y34, 
   z1, z2, z3, z4} ∈ Integers }

but it gives this error

Minimize::mixdom: Exact optimization with mixed real and integer variables is not yet implemented

there is no difference? why one is ok and one gives error

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  • $\begingroup$ Please edit your question to add the code you've tried. $\endgroup$
    – creidhne
    Commented Aug 11, 2021 at 22:21
  • $\begingroup$ From Mathematica output (v. 11.3): Maximize::mixdom: Exact optimization with mixed real and integer variables is not yet implemented. $\endgroup$ Commented Aug 12, 2021 at 2:04

2 Answers 2

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If you restrict the ranges of x and y, you can get the desired result with Maximize with conditions x==Floor[x] or x==IntegerPart[x] or .....

Do first Maximize[{x + y + z, x <= 10, y <= 12.5, z <= 100}, {x, y, z}, Reals] for Reals to get an impression how to restrict x and y.

Maximize[{x + y + z, 0 < x <= 10, 0 < y <= 125/10, z <= 100, 
           x==Floor[x] , y==Floor[y] }, {x, y, z}, Reals]

(*   {122, {x -> 10, y -> 12, z -> 100}}   *)

NMaximize[{x + y + z, x <= 10, y <= 12.5, z <= 100, 
    x \[Element] Integers, y \[Element] Integers, 
    z \[Element] Reals}, {x, y, z}]

(*   {122., {x -> 10, y -> 12, z -> 100.}}   *)
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With exact input (125/10 instead of 12.5), the first call fails:

Maximize[
{x + y + z, x <= 10, y <= 125/10, z <= 100},
{{x, z} \[Element] Integers, {y} \[Element] Reals}]

Maximize::mixdom: Exact optimization with mixed real and integer variables is not yet implemented.

With inexact input, NMaximize is called (see “Details” in documentation for Maximize):

Trace[
 Maximize[
  {x + y + z, x <= 10, y <= 12.5, z <= 100}, 
  {{x, z} \[Element] Integers, {y} \[Element] Reals}],
 _NMaximize,
 TraceInternal -> True
 ]

Mixed domain are not implemented for Maximize, but they are for NMaximize.

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