Fortran is a numeric beast, which is exactly why its still popular amongst scientific programmers. Languages like C are still somewhat constrained when it comes to numerical precision. In C, a long double gets you\u2026<\/p>\n\n\n\n
Fortran 90 and beyond provides a kind<\/strong> parameter which can be used to specify precision of both reals and integers. Fortran uses the function selected_real_kind()<\/strong> to create a parameter of real type for kind.<\/strong> Inputs to this are precision<\/em> and range<\/em>. Here is an example:<\/p>\n\n\n\n This produces a parameter, dp, used to define a double precision real with 15 significant digits, and an exponent range or 307. Single and quad precision can also be defined in a similar way:<\/p>\n\n\n\n In Fortran 2008, the constants real32<\/strong>, real64<\/strong>, and real128<\/strong> can be used instead of selected_real_kind(). How does this work? Consider the following piece of Fortran code to calculate the repeating decimal 1.0\/7.0. The answer should be 0.142857 142857\u2026 Note that the floating point numbers used have to be tagged as a specific kind (e.g. 1.0_dp<\/strong>), otherwise the outcome can be erroneous.<\/p>\n\n\n\n What happens when we run it in all three precisions?<\/p>\n\n\n\n The BOLD <\/strong>numbers show the precision of the number, with correct digits. The Underline numbers are those correct beyond the precision. Now compare this to C\u2019s long double<\/strong> which is typically 80-bit extended precision. Here\u2019s the C code:<\/p>\n\n\n\n Here\u2019s the result:<\/p>\n\n\n\n <\/p>\n","protected":false},"excerpt":{"rendered":" Fortran is a numeric beast, which is exactly why its still popular amongst scientific programmers. Languages like C are still somewhat constrained when it comes to numerical precision. In C, a long double gets you\u2026 Fortran 90 and beyond provides a kind parameter which can be used to specify precision of both reals and integers. Fortran uses […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2],"tags":[],"_links":{"self":[{"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/posts\/90"}],"collection":[{"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=90"}],"version-history":[{"count":2,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/posts\/90\/revisions"}],"predecessor-version":[{"id":93,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=\/wp\/v2\/posts\/90\/revisions\/93"}],"wp:attachment":[{"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=90"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=90"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/laserphotonics.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=90"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}integer, parameter :: dp = selected_real_kind(15, 307)\nreal (kind=dp) :: x, y<\/pre>\n\n\n\n
integer, parameter :: sp = selected_real_kind(6, 37)\ninteger, parameter :: qp = selected_real_kind(33, 4931)<\/pre>\n\n\n\n
integer, parameter :: dp = selected_real_kind(15, 307)\nreal (kind=dp) :: d\nd = 1.0_dp \/ 7.0_dp<\/pre>\n\n\n\n
SP = 0.142857<\/strong>14<\/span>924335479736328125000000000\n DP = 0.142857142857142<\/strong>8<\/span>4921269268124888185\n QP = 0.142857142857142857142857142857142<\/strong>85<\/span><\/pre>\n\n\n\nlong double d;\nd = 1.0L \/ 7.0L;<\/pre>\n\n\n\n
0.14285714285714285714<\/strong>09210675491330277964<\/pre>\n\n\n\n