7
$\begingroup$

I want to code that will do the following:

Write a Mathematica function called randomHop that takes as its argument a list containing two coordinates x and y; your definition should begin

randomHop[{x_, y_}] := 

The function should then generate a random integer r equal to 1 or 2 (this should be locally scoped), and then

  • if r is equal to 1, return {{0.5, 0.5}, {0.5, 0.5}} . {x, y};
  • if r is 2, return {{-0.5, -0.5}, {0.5, -0.5}} . {x, y} + {1.0, 0}.

I have so far tried

randomHop[{x_, y_}] := (
  r = RandomInteger[{1, 2}]
  If[r == 1, Return[{{0.5, 0.5}, {0.5, 0.5}}.{x, y}], 
  Return[{{-0.5, -0.5}, {0.5, -0.5}} . {x, y} + {1.0, 0}]])

but it's not working, and I don't know why. Any help would be appreciated.

$\endgroup$
2
  • 4
    $\begingroup$ does it work if you add a ; right after r = RandomInteger[{1, 2}] ? $\endgroup$
    – Nasser
    Dec 9, 2019 at 3:57
  • $\begingroup$ No it doesn't @Nasser $\endgroup$
    – Ganyo10
    Dec 9, 2019 at 18:24

2 Answers 2

7
$\begingroup$

To localize r, I would use Module. Otherwise, the only changes needed are inserting a missing semicolon and getting rid of the unnecessary Return calls.

ClearAll[randomHop];
randomHop[{x_,y_}]:=Module[{
    r
},
    r=RandomInteger[{1,2}];
    If[r==1,
        {{0.5,0.5},{0.5,0.5}}.{x,y},
        {{-0.5,-0.5},{0.5,-0.5}}.{x,y}+{1,0}
    ]
];

SeedRandom[1];

NestList[randomHop,{1,2},10];
{{1, 2}, {-0.5, -0.5}, {1.5, 0.}, {0.75, 0.75}, {0.25, 0.}, {0.125, 0.125}, 
 {0.125, 0.125}, {0.125, 0.125}, {0.875, 0.}, {0.4375, 0.4375}, {0.5625, 0.}}

Visualize the path like:

NestList[randomHop,{1,2},10]//ListLinePlot
$\endgroup$
3
  • $\begingroup$ I tried your suggestion and it still doesn't seem to work $\endgroup$
    – Ganyo10
    Dec 9, 2019 at 18:25
  • $\begingroup$ @Ganyo10. Your comment is opaque. My answer shows it worked fine form me. What went wrong when you ran my code in on your system? $\endgroup$
    – m_goldberg
    Dec 9, 2019 at 18:43
  • $\begingroup$ @Ganyo10 have you tried copying each statement in a separate cell? Maybe some parsing issue. $\endgroup$
    – user13892
    Dec 10, 2019 at 22:35
1
$\begingroup$
randomHop[{x_, y_}] := If[RandomInteger[{1, 2}] == 1, {{0.5, 0.5}, {0.5, 0.5}}.{x, y}, 
    {{-0.5, -0.5}, {0.5, -0.5}}.{x, y} + {1.0, 0}]

also works.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.