Set every element to zero in matrix unless it's `1` or `1/2`












1












$begingroup$


I have the following code:



max = 1;



PotentialTilde[V0_] := 

  SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 

    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1 }];



a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]] // 

  MatrixForm


That generates this matrix:



<span class=$$ $$">




How do I set every element that is not equal to 1 or 1/2 to 0?






list-manipulation matrix







share|improve this question











$endgroup$












  • $begingroup$
    Something like a /. {1 -> 0, 1/2 -> 0} should do it.
    $endgroup$
    – Carl Lange
    1 hour ago










  • $begingroup$
    Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
    $endgroup$
    – SuperCiocia
    1 hour ago










  • $begingroup$
    Also, your command does not change anything to my a
    $endgroup$
    – SuperCiocia
    1 hour ago






  • 1




    $begingroup$
    Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
    $endgroup$
    – Lukas Lang
    1 hour ago
















1












$begingroup$


I have the following code:



max = 1;



PotentialTilde[V0_] := 

  SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 

    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1 }];



a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]] // 

  MatrixForm


That generates this matrix:



<span class=$$ $$">




How do I set every element that is not equal to 1 or 1/2 to 0?






list-manipulation matrix







share|improve this question











$endgroup$












  • $begingroup$
    Something like a /. {1 -> 0, 1/2 -> 0} should do it.
    $endgroup$
    – Carl Lange
    1 hour ago










  • $begingroup$
    Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
    $endgroup$
    – SuperCiocia
    1 hour ago










  • $begingroup$
    Also, your command does not change anything to my a
    $endgroup$
    – SuperCiocia
    1 hour ago






  • 1




    $begingroup$
    Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
    $endgroup$
    – Lukas Lang
    1 hour ago














1












1








1





$begingroup$


I have the following code:



max = 1;



PotentialTilde[V0_] := 

  SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 

    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1 }];



a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]] // 

  MatrixForm


That generates this matrix:



<span class=$$ $$">




How do I set every element that is not equal to 1 or 1/2 to 0?






list-manipulation matrix







share|improve this question











$endgroup$




I have the following code:



max = 1;



PotentialTilde[V0_] := 

  SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 

    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1 }];



a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]] // 

  MatrixForm


That generates this matrix:



<span class=$$ $$">




How do I set every element that is not equal to 1 or 1/2 to 0?






list-manipulation matrix




list-manipulation matrix






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 36 mins ago









gwr

7,81322558




7,81322558










asked 1 hour ago









SuperCiociaSuperCiocia

515311




515311












  • $begingroup$
    Something like a /. {1 -> 0, 1/2 -> 0} should do it.
    $endgroup$
    – Carl Lange
    1 hour ago










  • $begingroup$
    Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
    $endgroup$
    – SuperCiocia
    1 hour ago










  • $begingroup$
    Also, your command does not change anything to my a
    $endgroup$
    – SuperCiocia
    1 hour ago






  • 1




    $begingroup$
    Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
    $endgroup$
    – Lukas Lang
    1 hour ago


















  • $begingroup$
    Something like a /. {1 -> 0, 1/2 -> 0} should do it.
    $endgroup$
    – Carl Lange
    1 hour ago










  • $begingroup$
    Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
    $endgroup$
    – SuperCiocia
    1 hour ago










  • $begingroup$
    Also, your command does not change anything to my a
    $endgroup$
    – SuperCiocia
    1 hour ago






  • 1




    $begingroup$
    Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
    $endgroup$
    – Lukas Lang
    1 hour ago
















$begingroup$
Something like a /. {1 -> 0, 1/2 -> 0} should do it.
$endgroup$
– Carl Lange
1 hour ago




$begingroup$
Something like a /. {1 -> 0, 1/2 -> 0} should do it.
$endgroup$
– Carl Lange
1 hour ago












$begingroup$
Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
$endgroup$
– SuperCiocia
1 hour ago




$begingroup$
Yeah, but I want the opposite. Anything that is NOT equal to 1 and 1/2
$endgroup$
– SuperCiocia
1 hour ago












$begingroup$
Also, your command does not change anything to my a
$endgroup$
– SuperCiocia
1 hour ago




$begingroup$
Also, your command does not change anything to my a
$endgroup$
– SuperCiocia
1 hour ago




1




1




$begingroup$
Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
$endgroup$
– Lukas Lang
1 hour ago




$begingroup$
Look up Except. Also, if you want to change a, you have to assign the result to a again. (In Mathematica, barely anything changes variables, most things are immutable)
$endgroup$
– Lukas Lang
1 hour ago










3 Answers
3






active

oldest

votes


















5












$begingroup$

Be careful with assigning a "form" (e.g. MatrixForm) to a variable. Another observation is that a is a SparseArray uses rules to store the values and since ReplaceAll works with the FullForm of an expression care has to be taken (using Normal will make the array a regular matrix again).



This should work: 



max = 1;

PotentialTilde[V0_] := SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 

    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1}];



a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];

(* a // MatrixForm *)



aMod = (a // Normal) /. x_?NumericQ /; Not@MatchQ[x, 1 | 1/2] -> 0;

aMod // MatrixForm


Matrix



Lukas Lang's suggestion is even nicer:



aMod = (a // Normal) /. Except[1 | 1/2, _?NumericQ] -> 0;





share|improve this answer











$endgroup$













  • $begingroup$
    Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
    $endgroup$
    – Henrik Schumacher
    26 mins ago





















2












$begingroup$

a cannot be a MatrixForm:



(a = KroneckerProduct[PotentialTilde[1], 

    PotentialTilde[1]]) // MatrixForm


Convert to a regular Matrix:



Normal[a] /. {ij_ /; (NumberQ[

       ij] && ( ij != 1/2 && ij != 1)) :> 0}



(a = Normal[

     a] /. {ij_ /; (NumberQ[

          ij] && ( ij != 1/2 && ij != 1)) :> 

      0}) // MatrixForm

a



MatrixForm[a]





share|improve this answer









$endgroup$





















    2












    $begingroup$

    A = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
    
B = A (1 - Unitize[A - 1/2] Unitize[A - 1]);
    
B // MatrixForm







    share|improve this answer











    $endgroup$













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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      5












      $begingroup$

      Be careful with assigning a "form" (e.g. MatrixForm) to a variable. Another observation is that a is a SparseArray uses rules to store the values and since ReplaceAll works with the FullForm of an expression care has to be taken (using Normal will make the array a regular matrix again).



      This should work: 



      max = 1;
      
PotentialTilde[V0_] := SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 
      
    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1}];
      

      
a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
      
(* a // MatrixForm *)
      

      
aMod = (a // Normal) /. x_?NumericQ /; Not@MatchQ[x, 1 | 1/2] -> 0;
      
aMod // MatrixForm


      Matrix



      Lukas Lang's suggestion is even nicer:



      aMod = (a // Normal) /. Except[1 | 1/2, _?NumericQ] -> 0;





      share|improve this answer











      $endgroup$













      • $begingroup$
        Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
        $endgroup$
        – Henrik Schumacher
        26 mins ago


















      5












      $begingroup$

      Be careful with assigning a "form" (e.g. MatrixForm) to a variable. Another observation is that a is a SparseArray uses rules to store the values and since ReplaceAll works with the FullForm of an expression care has to be taken (using Normal will make the array a regular matrix again).



      This should work: 



      max = 1;
      
PotentialTilde[V0_] := SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 
      
    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1}];
      

      
a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
      
(* a // MatrixForm *)
      

      
aMod = (a // Normal) /. x_?NumericQ /; Not@MatchQ[x, 1 | 1/2] -> 0;
      
aMod // MatrixForm


      Matrix



      Lukas Lang's suggestion is even nicer:



      aMod = (a // Normal) /. Except[1 | 1/2, _?NumericQ] -> 0;





      share|improve this answer











      $endgroup$













      • $begingroup$
        Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
        $endgroup$
        – Henrik Schumacher
        26 mins ago
















      5












      5








      5





      $begingroup$

      Be careful with assigning a "form" (e.g. MatrixForm) to a variable. Another observation is that a is a SparseArray uses rules to store the values and since ReplaceAll works with the FullForm of an expression care has to be taken (using Normal will make the array a regular matrix again).



      This should work: 



      max = 1;
      
PotentialTilde[V0_] := SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 
      
    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1}];
      

      
a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
      
(* a // MatrixForm *)
      

      
aMod = (a // Normal) /. x_?NumericQ /; Not@MatchQ[x, 1 | 1/2] -> 0;
      
aMod // MatrixForm


      Matrix



      Lukas Lang's suggestion is even nicer:



      aMod = (a // Normal) /. Except[1 | 1/2, _?NumericQ] -> 0;





      share|improve this answer











      $endgroup$



      Be careful with assigning a "form" (e.g. MatrixForm) to a variable. Another observation is that a is a SparseArray uses rules to store the values and since ReplaceAll works with the FullForm of an expression care has to be taken (using Normal will make the array a regular matrix again).



      This should work: 



      max = 1;
      
PotentialTilde[V0_] := SparseArray[{Band[{1, 1}] -> V0/1, Band[{2, 1}] -> V0/2, 
      
    Band[{1, 2}] -> V0/2}, {2*max + 1, 2*max + 1}];
      

      
a = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
      
(* a // MatrixForm *)
      

      
aMod = (a // Normal) /. x_?NumericQ /; Not@MatchQ[x, 1 | 1/2] -> 0;
      
aMod // MatrixForm


      Matrix



      Lukas Lang's suggestion is even nicer:



      aMod = (a // Normal) /. Except[1 | 1/2, _?NumericQ] -> 0;






      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited 48 mins ago

























      answered 1 hour ago









      gwrgwr

      7,81322558




      7,81322558












      • $begingroup$
        Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
        $endgroup$
        – Henrik Schumacher
        26 mins ago




















      • $begingroup$
        Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
        $endgroup$
        – Henrik Schumacher
        26 mins ago


















      $begingroup$
      Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
      $endgroup$
      – Henrik Schumacher
      26 mins ago






      $begingroup$
      Huh, never apply Normal to SparseArrays. Hell might break loose... ;) (Anyways, +1 of course.)
      $endgroup$
      – Henrik Schumacher
      26 mins ago













      2












      $begingroup$

      a cannot be a MatrixForm:



      (a = KroneckerProduct[PotentialTilde[1], 
      
    PotentialTilde[1]]) // MatrixForm


      Convert to a regular Matrix:



      Normal[a] /. {ij_ /; (NumberQ[
      
       ij] && ( ij != 1/2 && ij != 1)) :> 0}
      

      
(a = Normal[
      
     a] /. {ij_ /; (NumberQ[
      
          ij] && ( ij != 1/2 && ij != 1)) :> 
      
      0}) // MatrixForm
      
a
      

      
MatrixForm[a]





      share|improve this answer









      $endgroup$


















        2












        $begingroup$

        a cannot be a MatrixForm:



        (a = KroneckerProduct[PotentialTilde[1], 
        
    PotentialTilde[1]]) // MatrixForm


        Convert to a regular Matrix:



        Normal[a] /. {ij_ /; (NumberQ[
        
       ij] && ( ij != 1/2 && ij != 1)) :> 0}
        

        
(a = Normal[
        
     a] /. {ij_ /; (NumberQ[
        
          ij] && ( ij != 1/2 && ij != 1)) :> 
        
      0}) // MatrixForm
        
a
        

        
MatrixForm[a]





        share|improve this answer









        $endgroup$
















          2












          2








          2





          $begingroup$

          a cannot be a MatrixForm:



          (a = KroneckerProduct[PotentialTilde[1], 
          
    PotentialTilde[1]]) // MatrixForm


          Convert to a regular Matrix:



          Normal[a] /. {ij_ /; (NumberQ[
          
       ij] && ( ij != 1/2 && ij != 1)) :> 0}
          

          
(a = Normal[
          
     a] /. {ij_ /; (NumberQ[
          
          ij] && ( ij != 1/2 && ij != 1)) :> 
          
      0}) // MatrixForm
          
a
          

          
MatrixForm[a]





          share|improve this answer









          $endgroup$



          a cannot be a MatrixForm:



          (a = KroneckerProduct[PotentialTilde[1], 
          
    PotentialTilde[1]]) // MatrixForm


          Convert to a regular Matrix:



          Normal[a] /. {ij_ /; (NumberQ[
          
       ij] && ( ij != 1/2 && ij != 1)) :> 0}
          

          
(a = Normal[
          
     a] /. {ij_ /; (NumberQ[
          
          ij] && ( ij != 1/2 && ij != 1)) :> 
          
      0}) // MatrixForm
          
a
          

          
MatrixForm[a]






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 40 mins ago









          Craig CarterCraig Carter

          499412




          499412























              2












              $begingroup$

              A = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
              
B = A (1 - Unitize[A - 1/2] Unitize[A - 1]);
              
B // MatrixForm







              share|improve this answer











              $endgroup$


















                2












                $begingroup$

                A = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
                
B = A (1 - Unitize[A - 1/2] Unitize[A - 1]);
                
B // MatrixForm







                share|improve this answer











                $endgroup$
















                  2












                  2








                  2





                  $begingroup$

                  A = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
                  
B = A (1 - Unitize[A - 1/2] Unitize[A - 1]);
                  
B // MatrixForm







                  share|improve this answer











                  $endgroup$



                  A = KroneckerProduct[PotentialTilde[1], PotentialTilde[1]];
                  
B = A (1 - Unitize[A - 1/2] Unitize[A - 1]);
                  
B // MatrixForm








                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited 16 mins ago

























                  answered 33 mins ago









                  Henrik SchumacherHenrik Schumacher

                  50.5k469144




                  50.5k469144






























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