double
converts inttype integers or booleans into decimal encoding
Syntax
y = double(X)
Arguments
- X
matrix of encoded integers or booleans
- y
matrix of numbers in decimal notation
Description
converts data stored using 1, 2, 4 or 8 bytes integers into
decimal representation on 8 bytes. If X
entries are already double precision floats, nothing is done.
 |
|
| Booleans can also be processed with |
 | Since the mantissa of |
Examples
x = int8([0 12 140]) double(x) // Applying double() rounds off and truncates int64() or uint64() numbers // ---------------------------------------------------------------------- i = int64(2)^52 // 52 bits, as for decimal numbers mantissa i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] err = i - double(i) // no errors for |integers|<= 2^52 i = int64(2)^53 // 53 bits integers => more accurate than decimal numbers i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] err = i - double(i) // round-off errors appear i = int64(2)^55 i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] err = i - double(i) i = int64(2)^62 i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] err = i - double(i)
--> i = int64(2)^52 // 52 bits, as for decimal numbers mantissa i = 4503599627370496 --> i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] i = 4503599627370496 4503599627370499 4503599627370526 4503599627370499 4503599627370529 4503599627370826 4503599627370502 4503599627370559 4503599627371126 4503599627370505 4503599627370589 4503599627371426 --> err = i - double(i) // no errors for |integers|<= 2^52 err = 0 0 0 0 0 0 0 0 0 0 0 0 --> i = int64(2)^53 // 53 bits integers => more accurate than decimal numbers i = 9007199254740992 --> i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] i = 9007199254740992 9007199254740995 9007199254741022 9007199254740995 9007199254741025 9007199254741322 9007199254740998 9007199254741055 9007199254741622 9007199254741001 9007199254741085 9007199254741922 --> err = i - double(i) // round-off errors appear err = 0 -1 0 -1 1 0 0 -1 0 1 1 0 --> i = int64(2)^55 i = 36028797018963968 --> i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] i = 36028797018963968 36028797018963971 36028797018963998 36028797018963971 36028797018964001 36028797018964298 36028797018963974 36028797018964031 36028797018964598 36028797018963977 36028797018964061 36028797018964898 --> err = i - double(i) err = 0 3 -2 3 1 2 -2 -1 -2 1 -3 2 --> i = int64(2)^62 i = 4611686018427387904 --> i = [i+(0:3:9)' i+(3:30:93)' i+(30:300:930)'] i = 4611686018427387904 4611686018427387907 4611686018427387934 4611686018427387907 4611686018427387937 4611686018427388234 4611686018427387910 4611686018427387967 4611686018427388534 4611686018427387913 4611686018427387997 4611686018427388834 --> err = i - double(i) err = 0 3 30 3 33 330 6 63 -394 9 93 -94
// Comparing speeds of double(), bool2s() and iconvert(,0) on booleans // ------------------------------------------------------------------- b = (rand(1000,1000)<0.5); tic(),for i=1:100, bool2s(b); end, toc() tic(),for i=1:100, double(b); end, toc() tic(),for i=1:100, iconvert(b,0); end, toc()
--> b = (rand(1000,1000)<0.5); --> tic(),for i=1:100, bool2s(b); end, toc() ans = 1.1680533 --> tic(),for i=1:100, double(b); end, toc() ans = 2.9003021 --> tic(),for i=1:100, iconvert(b,0); end, toc() ans = 2.1867567
// Speed comparison between double() and iconvert(..,0) on int32 integers // ---------------------------------------------------------------------- i = int32((rand(1000,1000)-0.5)*1000); tic(),for j=1:100, double(i); end, toc() tic(),for j=1:100, iconvert(i,0); end, toc()
--> i = int32((rand(1000,1000)-0.5)*10000); --> tic(),for j=1:100, double(i); end, toc() ans = 2.2464656 --> tic(),for j=1:100, iconvert(i,0); end, toc() ans = 2.2771408
See also
History
| バージョン | 記述 |
| 6.0 | New int64 and uint64 encoded integers can now be converted. |
| Report an issue | ||
| << clean | Floating point | fix >> |