Skip to main content

Using multiple solutions from equations in further calculations


First: This question is a follow-up question to my question here.


Consider the following code with output:


ClearAll[a1, b1, a2, b2, xC1, yC1, xC2, yC2, c, m]
a1 := 2
b1 := 1
a2 := 1
b2 := 1/2
xC1 := 0
yC1 := 1

xC2 := 0
yC2 := 4

eqn1 = a1 (a1^2 b2^2 m^2 + b1^2 (b2^2 - (c + m xC1 - yC1)^2)) ==
b2 (a1^2 (a2^2 m^2 + b2^2) - a2^2 (c + m xC2 - yC2)^2);
eqn2 = (a1^2 m (c - yC1) - b1^2 xC1)^2 ==
(a1^2 m^2 + b1^2) (b1^2 xC1^2 + a1^2 (c - yC1)^2 - a1^2 b2^2);
Solve[eqn1 && eqn2, {c, m}]

\begin{equation} \small \left\{ \left\{c \to -2, m \to -\frac{\sqrt{35}}{2}\right\}, \left\{c \to -2, m \to \frac{\sqrt{35}}{2}\right\}, \left\{c \to 2, m \to -\frac{\sqrt{3}}{2}\right\}, \left\{c \to 2, m \to \frac{\sqrt{3}}{2}\right\} \right\} \end{equation}



I need to calculate the values of the two expressions


(a1^2 m (c - yC1) - b1^2 xC1)/(a1^2 m^2 + b1^2)
(a2^2 m (c - yC2) - b2^2 xC2)/(a2^2 m^2 + b2^2)

for all four combinations of $c$ and $m$. (This gives eight output values.)


Furthermore, I would like the eight output values to be named x1 to x8.


How do I do that?



Answer



ClearAll[a1, b1, a2, b2, xC1, yC1, xC2, yC2, c, m]
a1 = 2;

b1 = 1;
a2 = 1;
b2 = 1/2;
xC1 = 0;
yC1 = 1;
xC2 = 0;
yC2 = 4;

eqn1 = a1 (a1^2 b2^2 m^2 + b1^2 (b2^2 - (c + m xC1 - yC1)^2)) ==
b2 (a1^2 (a2^2 m^2 + b2^2) - a2^2 (c + m xC2 - yC2)^2);

eqn2 = (a1^2 m (c - yC1) - b1^2 xC1)^2 == (a1^2 m^2 + b1^2) (b1^2 xC1^2 +
a1^2 (c - yC1)^2 - a1^2 b2^2);

sol = Solve[eqn1 && eqn2, {c, m}];

Clear[x]

Using an indexed variable and depending on the order of the sequencing desired, use either


Evaluate[Array[x, 8]] = {(a1^2 m (c - yC1) - b1^2 xC1)/(a1^2 m^2 + b1^2),
(a2^2 m (c - yC2) - b2^2 xC2)/(a2^2 m^2 + b2^2)} /. sol // Flatten;


x /@ Range[8]

(* {Sqrt[35]/6, Sqrt[35]/3, -(Sqrt[35]/6), -(Sqrt[35]/3), -(Sqrt[3]/
2), Sqrt[3], Sqrt[3]/2, -Sqrt[3]} *)

or


Clear[x]

Evaluate[Array[x, 8]] = {(a1^2 m (c - yC1) - b1^2 xC1)/(a1^2 m^2 + b1^2),

(a2^2 m (c - yC2) - b2^2 xC2)/(a2^2 m^2 + b2^2)} /. sol // Transpose //
Flatten;

x /@ Range[8]

(* {Sqrt[35]/6, -(Sqrt[35]/6), -(Sqrt[3]/2), Sqrt[3]/2, Sqrt[35]/3, -(Sqrt[35]/
3), Sqrt[3], -Sqrt[3]} *)

Comments

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...

How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : tdata = {{{a1, b1}, {a2, b2}}, {{a1, c1}, {a2, c2}}, {{a1, d1}, {a2, d2}}} Tableform: And I would like to do better then pseudofunction[n_] := Transpose[{data2[[1]], data2[[n]]}]; SetAttributes[pseudofunction, Listable]; Range[2, 4] // pseudofunction Here is my benchmark data, where data3 is normal sample of real data. data3 = Drop[ExcelWorkBook[[Column1 ;; Column4]], None, 1]; data2 = {a #, b #, c #, d #} & /@ Range[1, 10^5]; data = RandomReal[{0, 1}, {10^6, 4}]; Here is my benchmark code kptnw[list_] := Transpose[{Table[First@#, {Length@# - 1}], Rest@#}, {3, 1, 2}] &@list kptnw2[list_] := Transpose[{ConstantArray[First@#, Length@# - 1], Rest@#}, {3, 1, 2}] &@list OleksandrR[list_] := Flatten[Outer[List, List@First[list], Rest[list], 1], {{2}, {1, 4}}] paradox2[list_] := Partition[Riffle[list[[1]], #], 2] & /@ Drop[list, 1] RM[list_] := FoldList[Transpose[{First@li...

front end - keyboard shortcut to invoke Insert new matrix

I frequently need to type in some matrices, and the menu command Insert > Table/Matrix > New... allows matrices with lines drawn between columns and rows, which is very helpful. I would like to make a keyboard shortcut for it, but cannot find the relevant frontend token command (4209405) for it. Since the FullForm[] and InputForm[] of matrices with lines drawn between rows and columns is the same as those without lines, it's hard to do this via 3rd party system-wide text expanders (e.g. autohotkey or atext on mac). How does one assign a keyboard shortcut for the menu item Insert > Table/Matrix > New... , preferably using only mathematica? Thanks! Answer In the MenuSetup.tr (for linux located in the $InstallationDirectory/SystemFiles/FrontEnd/TextResources/X/ directory), I changed the line MenuItem["&New...", "CreateGridBoxDialog"] to read MenuItem["&New...", "CreateGridBoxDialog", MenuKey["m", Modifiers-...