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Number of computations for multiplication


Fast algorithm for matrix chain multiplication in special caseWhy is the transform in Schönhage–Strassen's multiplication algorithm cheap?Shouldn't complexity theory consider the time taken for different operations?Fixed base exponentiation with precomputationsAre there any non-naive parallel sparse matrix multiplication algorithms?Controlling overflow and loss of precision during floating point multiplicationDividing/Multiplying Numbers Stored in two memory locationsHow many basic operations are there in an algorithm for the simple multiplication of two numbers of equal length?Long multiplication school method: number of primitive operations to calculate first partial product?Are all computational complexity results oracle results?













3












$begingroup$


I just read Marvin Minskys' "Form and Content in Computer Science" and found myself confused with the following paragraph:




A startling discovery was made about multiplication itself in the
thesis of S.A. Cook [3], which uses a result of A.L. Toom, as
discussed in Knuth [4]. Consider the ordinary algorithm for
multiplying decimal numbers: for two n-digit numbers this employs
n-squared one-digit products. It is usually supposed that this is
minimal. But suppose we write the numbers in two halves, so that the
product is N = (#A+B)(#C+D), where # stands for multiplying by 10 subscript{n/2}.
(The left-shift operation is considered to have negligible cost.) Then
one can verify that



N = ##AC + BD + #(A+B)(C+D) - #(AC+BD).



This involves only three half-length multiplications, instead of the
four that one might suppose were needed. For large n, the reduction
can obviously be reapplied over and over to the smaller numbers. The
price is a growing number of additions. By compounding this and other
ideas, Cook showed that for any e and large enough n, multiplication
requires less than n*(1-e) products, instead of the expected
n-squared.




I got stuck when I read stands for multiplying by 10 ... because I didn't understand what the subscript in this example means. I tried to find it out by googling about the complexity of multiplication and stuff like that, but couldn't find the answer.



Can you point me in the right direction here? I guess that this exact part is essential for understanding the formula in the middle. I would like to find out how this computation would resolve a multiplication.










share|cite|improve this question







New contributor




Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$

















    3












    $begingroup$


    I just read Marvin Minskys' "Form and Content in Computer Science" and found myself confused with the following paragraph:




    A startling discovery was made about multiplication itself in the
    thesis of S.A. Cook [3], which uses a result of A.L. Toom, as
    discussed in Knuth [4]. Consider the ordinary algorithm for
    multiplying decimal numbers: for two n-digit numbers this employs
    n-squared one-digit products. It is usually supposed that this is
    minimal. But suppose we write the numbers in two halves, so that the
    product is N = (#A+B)(#C+D), where # stands for multiplying by 10 subscript{n/2}.
    (The left-shift operation is considered to have negligible cost.) Then
    one can verify that



    N = ##AC + BD + #(A+B)(C+D) - #(AC+BD).



    This involves only three half-length multiplications, instead of the
    four that one might suppose were needed. For large n, the reduction
    can obviously be reapplied over and over to the smaller numbers. The
    price is a growing number of additions. By compounding this and other
    ideas, Cook showed that for any e and large enough n, multiplication
    requires less than n*(1-e) products, instead of the expected
    n-squared.




    I got stuck when I read stands for multiplying by 10 ... because I didn't understand what the subscript in this example means. I tried to find it out by googling about the complexity of multiplication and stuff like that, but couldn't find the answer.



    Can you point me in the right direction here? I guess that this exact part is essential for understanding the formula in the middle. I would like to find out how this computation would resolve a multiplication.










    share|cite|improve this question







    New contributor




    Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$















      3












      3








      3





      $begingroup$


      I just read Marvin Minskys' "Form and Content in Computer Science" and found myself confused with the following paragraph:




      A startling discovery was made about multiplication itself in the
      thesis of S.A. Cook [3], which uses a result of A.L. Toom, as
      discussed in Knuth [4]. Consider the ordinary algorithm for
      multiplying decimal numbers: for two n-digit numbers this employs
      n-squared one-digit products. It is usually supposed that this is
      minimal. But suppose we write the numbers in two halves, so that the
      product is N = (#A+B)(#C+D), where # stands for multiplying by 10 subscript{n/2}.
      (The left-shift operation is considered to have negligible cost.) Then
      one can verify that



      N = ##AC + BD + #(A+B)(C+D) - #(AC+BD).



      This involves only three half-length multiplications, instead of the
      four that one might suppose were needed. For large n, the reduction
      can obviously be reapplied over and over to the smaller numbers. The
      price is a growing number of additions. By compounding this and other
      ideas, Cook showed that for any e and large enough n, multiplication
      requires less than n*(1-e) products, instead of the expected
      n-squared.




      I got stuck when I read stands for multiplying by 10 ... because I didn't understand what the subscript in this example means. I tried to find it out by googling about the complexity of multiplication and stuff like that, but couldn't find the answer.



      Can you point me in the right direction here? I guess that this exact part is essential for understanding the formula in the middle. I would like to find out how this computation would resolve a multiplication.










      share|cite|improve this question







      New contributor




      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      I just read Marvin Minskys' "Form and Content in Computer Science" and found myself confused with the following paragraph:




      A startling discovery was made about multiplication itself in the
      thesis of S.A. Cook [3], which uses a result of A.L. Toom, as
      discussed in Knuth [4]. Consider the ordinary algorithm for
      multiplying decimal numbers: for two n-digit numbers this employs
      n-squared one-digit products. It is usually supposed that this is
      minimal. But suppose we write the numbers in two halves, so that the
      product is N = (#A+B)(#C+D), where # stands for multiplying by 10 subscript{n/2}.
      (The left-shift operation is considered to have negligible cost.) Then
      one can verify that



      N = ##AC + BD + #(A+B)(C+D) - #(AC+BD).



      This involves only three half-length multiplications, instead of the
      four that one might suppose were needed. For large n, the reduction
      can obviously be reapplied over and over to the smaller numbers. The
      price is a growing number of additions. By compounding this and other
      ideas, Cook showed that for any e and large enough n, multiplication
      requires less than n*(1-e) products, instead of the expected
      n-squared.




      I got stuck when I read stands for multiplying by 10 ... because I didn't understand what the subscript in this example means. I tried to find it out by googling about the complexity of multiplication and stuff like that, but couldn't find the answer.



      Can you point me in the right direction here? I guess that this exact part is essential for understanding the formula in the middle. I would like to find out how this computation would resolve a multiplication.







      complexity-theory multiplication






      share|cite|improve this question







      New contributor




      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|cite|improve this question







      New contributor




      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|cite|improve this question




      share|cite|improve this question






      New contributor




      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked 10 hours ago









      Fabian SchneiderFabian Schneider

      183




      183




      New contributor




      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.





      New contributor





      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






      Fabian Schneider is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






















          2 Answers
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          3












          $begingroup$

          It should be "10 superscript{n/2}" meaning $10^{n/2}$. For example, if $n=4$, then "6#2" would represent $6cdot10^2=600$. All he's doing is shifting a decimal number to the left.






          share|cite|improve this answer









          $endgroup$





















            3












            $begingroup$

            From context it's just exponentiation. I don't know why it's written with a subscript instead of a superscript, but with older papers you sometimes had a professional typesetter who might not have understood the material. (Of course nowadays typically do their own typesetting.)






            share|cite|improve this answer









            $endgroup$













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              $begingroup$

              It should be "10 superscript{n/2}" meaning $10^{n/2}$. For example, if $n=4$, then "6#2" would represent $6cdot10^2=600$. All he's doing is shifting a decimal number to the left.






              share|cite|improve this answer









              $endgroup$


















                3












                $begingroup$

                It should be "10 superscript{n/2}" meaning $10^{n/2}$. For example, if $n=4$, then "6#2" would represent $6cdot10^2=600$. All he's doing is shifting a decimal number to the left.






                share|cite|improve this answer









                $endgroup$
















                  3












                  3








                  3





                  $begingroup$

                  It should be "10 superscript{n/2}" meaning $10^{n/2}$. For example, if $n=4$, then "6#2" would represent $6cdot10^2=600$. All he's doing is shifting a decimal number to the left.






                  share|cite|improve this answer









                  $endgroup$



                  It should be "10 superscript{n/2}" meaning $10^{n/2}$. For example, if $n=4$, then "6#2" would represent $6cdot10^2=600$. All he's doing is shifting a decimal number to the left.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 9 hours ago









                  Rick DeckerRick Decker

                  12.7k33044




                  12.7k33044























                      3












                      $begingroup$

                      From context it's just exponentiation. I don't know why it's written with a subscript instead of a superscript, but with older papers you sometimes had a professional typesetter who might not have understood the material. (Of course nowadays typically do their own typesetting.)






                      share|cite|improve this answer









                      $endgroup$


















                        3












                        $begingroup$

                        From context it's just exponentiation. I don't know why it's written with a subscript instead of a superscript, but with older papers you sometimes had a professional typesetter who might not have understood the material. (Of course nowadays typically do their own typesetting.)






                        share|cite|improve this answer









                        $endgroup$
















                          3












                          3








                          3





                          $begingroup$

                          From context it's just exponentiation. I don't know why it's written with a subscript instead of a superscript, but with older papers you sometimes had a professional typesetter who might not have understood the material. (Of course nowadays typically do their own typesetting.)






                          share|cite|improve this answer









                          $endgroup$



                          From context it's just exponentiation. I don't know why it's written with a subscript instead of a superscript, but with older papers you sometimes had a professional typesetter who might not have understood the material. (Of course nowadays typically do their own typesetting.)







                          share|cite|improve this answer












                          share|cite|improve this answer



                          share|cite|improve this answer










                          answered 9 hours ago









                          Daniel McLauryDaniel McLaury

                          48427




                          48427






















                              Fabian Schneider is a new contributor. Be nice, and check out our Code of Conduct.










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