digitalmars.D.learn - pi program
- Charanjit Singh (17/17) Sep 24 2015 import std.stdio;
- Nicholas Wilson (7/24) Sep 24 2015 t=1/( n*n); //<----
- Russel Winder via Digitalmars-d-learn (77/105) Sep 25 2015 This looks a bit like K&R C transliterated to D. Much better to write
- mzfhhhh (5/12) Sep 25 2015 it should be write :
- Russel Winder via Digitalmars-d-learn (29/45) Sep 25 2015 Aha, bingo, spot on. Thanks. Amended now to:
- John Colvin (4/24) Sep 25 2015 I vastly prefer the UFCS version, but unfortunately reduce has
- Russel Winder via Digitalmars-d-learn (15/19) Sep 25 2015 [=E2=80=A6]
- John Colvin (7/17) Sep 26 2015 It's been argued about a lot.
- Russel Winder via Digitalmars-d-learn (17/24) Sep 28 2015 I guess the summary is: it's a breaking change, so do it. No we can't
- John Colvin (4/12) Sep 28 2015 My thoughts exactly, even though it was partly me that pointed
- Russel Winder via Digitalmars-d-learn (18/22) Sep 28 2015 [=E2=80=A6]
- Meta (4/21) Sep 25 2015 The main difference is that "method call" style is more amenable
- Russel Winder via Digitalmars-d-learn (13/18) Sep 28 2015 I guess coming from Clojure I was less worried about Lisp-style code.
import std.stdio;
import std.math;
void main()
{
float sum,pi,t;
int n=1;
sum=0;
while (n<100 )
{
t=1/( n*n);
n=n+1;
sum=sum+t;
}
writeln("value of PI= " , (sum*6)^^.5);
that is pi program as
(pi^2)/6= 1/1+ 1/4 + 1/9 + 1/16 + 1/25
but output of my program is 2.44
Sep 24 2015
On Friday, 25 September 2015 at 05:50:58 UTC, Charanjit Singh
wrote:
import std.stdio;
import std.math;
void main()
{
float sum,pi,t;
int n=1;
sum=0;
while (n<100 )
{
t=1/( n*n);
n=n+1;
sum=sum+t;
}
writeln("value of PI= " , (sum*6)^^.5);
that is pi program as
(pi^2)/6= 1/1+ 1/4 + 1/9 + 1/16 + 1/25
but output of my program is 2.44
t=1/( n*n); //<----
Is doing integer division so is zero for n > 1 hence sqrt(1*6) =
2.449...
change that to a
t=1.0/( n*n);
Sep 24 2015
On Fri, 2015-09-25 at 06:02 +0000, Nicholas Wilson via Digitalmars-d -learn wrote:On Friday, 25 September 2015 at 05:50:58 UTC, Charanjit Singh=20 wrote:This looks a bit like K&R C transliterated to D. Much better to write more idiomatic D=E2=80=A6import std.stdio; import std.math; void main() =20 { float sum,pi,t; int n=3D1; sum=3D0; while (n<100 ) { t=3D1/( n*n); n=3Dn+1; sum=3Dsum+t; =20 =20 } writeln("value of PI=3D " , (sum*6)^^.5); that is pi program as (pi^2)/6=3D 1/1+ 1/4 + 1/9 + 1/16 + 1/25 but output of my program is 2.44t=3D1/( n*n); //<---- Is doing integer division so is zero for n > 1 hence sqrt(1*6) =3D=20 2.449... =20 change that to a t=3D1.0/( n*n);That certainly solves the immediate problem. Taking the original code and making it more D-like, you get something like: double while_loop() { auto n =3D 1; auto sum =3D 0.0; while (n < 100) { sum +=3D 1.0 / (n * n); n++; } return sum; } but this is bounded iteration not unbounded iteration, so let us use a far more idiomatic form: double foreach_loop() { auto sum =3D 0.0; foreach (n; 1..100) { sum +=3D 1.0 / (n * n); } return sum; } but this is still very explicit iteration and we have moved on to the era of implicit iteration and declarative rather than imperative expression: double reduce_loop() { return reduce!"1.0 / (a * a)"(iota(1, 100)); } Unfortunately I have clearly done something silly here as: double take_root(double x) { return (x * 6)^^0.5; } void main() { writeln("while =3D " , take_root(while_loop())); writeln("foreach =3D " , take_root(foreach_loop())); writeln("reduce =3D " , take_root(reduce_loop())); } results in: while =3D 3.13198 foreach =3D 3.13198 reduce =3D 2.44949 If we worry about the string form and instead try: double reduce_string_loop() { return reduce!"1.0 / (a * a)"(iota(1, 100)); } double reduce_function_loop() { return reduce!((n) =3D> 1.0 / (n * n))(iota(1, 100)); } then we end up with: /usr/include/dmd/phobos/std/algorithm/iteration.d(2565): Error: template pi= _sumInverseSquares.reduce_function_loop.__lambda1 cannot deduce function fr= om argument types !()(int, int), candidates are: pi_sumInverseSquares.d(28): pi_sumInverseSquares.reduce_function_loo= p.__lambda1 /usr/include/dmd/phobos/std/meta.d(546): Error: template instance pi_sumInv= erseSquares.reduce_function_loop.F!(__lambda1) error instantiating /usr/include/dmd/phobos/std/algorithm/iteration.d(2473): instantiate= d from here: staticMap!(ReduceSeedType, __lambda1) pi_sumInverseSquares.d(28): instantiated from here: reduce!(Result) pi_sumInverseSquares.d(28): Error: template std.algorithm.iteration.reduce = cannot deduce function from argument types !((n) =3D> 1.00000 / (n * n))(Re= sult), candidates are: /usr/include/dmd/phobos/std/algorithm/iteration.d(2447): std.algorit= hm.iteration.reduce(fun...) if (fun.length >=3D 1) Failed: ["dmd", "-v", "-o-", "pi_sumInverseSquares.d", "-I."] which is sort of annoying. --=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
Sep 25 2015
If we worry about the string form and instead try:
double reduce_string_loop() {
return reduce!"1.0 / (a * a)"(iota(1, 100));
}
double reduce_function_loop() {
return reduce!((n) => 1.0 / (n * n))(iota(1, 100));
}
it should be write :
double reduce_loop() {
//return iota(1, 100).map!"1.0 / (a * a)".sum;
return iota(1, 100).reduce!"a + 1.0 / (b * b)";
}
Sep 25 2015
On Fri, 2015-09-25 at 09:14 +0000, mzfhhhh via Digitalmars-d-learn wrote:Aha, bingo, spot on. Thanks. Amended now to: double reduce_string_loop() { return reduce!"a + 1.0 / (b * b)"(iota(1, 100)); } double reduce_function_loop() { return reduce!((t, n) =3D> t + 1.0 / (n * n))(iota(1, 100)); } which both work as they should. I am sure I will be able to find a reason why I missed that reduce takes a function of two parameters not one. Interesting question on style is whether to use function application or method call: reduce!"a + 1.0 / (b * b)"(iota(1, 100)) vs. iota(1, 100).reduce!"a + 1.0 / (b * b)" The debate may well turn into a bikeshed one, but it would be good to know what the opinions are.=20 --=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winderIf we worry about the string form and instead try: =20 double reduce_string_loop() { return reduce!"1.0 / (a * a)"(iota(1, 100)); } =20 double reduce_function_loop() { return reduce!((n) =3D> 1.0 / (n * n))(iota(1, 100)); } =20=20 it should be write : double reduce_loop() { //return iota(1, 100).map!"1.0 / (a * a)".sum; return iota(1, 100).reduce!"a + 1.0 / (b * b)"; }
Sep 25 2015
On Friday, 25 September 2015 at 12:51:17 UTC, Russel Winder wrote:On Fri, 2015-09-25 at 09:14 +0000, mzfhhhh via Digitalmars-d-learn wrote:I vastly prefer the UFCS version, but unfortunately reduce has its arguments the wrong way around for that if you use the version that takes a seed...[...]Aha, bingo, spot on. Thanks. Amended now to: double reduce_string_loop() { return reduce!"a + 1.0 / (b * b)"(iota(1, 100)); } double reduce_function_loop() { return reduce!((t, n) => t + 1.0 / (n * n))(iota(1, 100)); } which both work as they should. I am sure I will be able to find a reason why I missed that reduce takes a function of two parameters not one. Interesting question on style is whether to use function application or method call: reduce!"a + 1.0 / (b * b)"(iota(1, 100)) vs. iota(1, 100).reduce!"a + 1.0 / (b * b)" The debate may well turn into a bikeshed one, but it would be good to know what the opinions are.
Sep 25 2015
On Fri, 2015-09-25 at 12:54 +0000, John Colvin via Digitalmars-d-learn wrote:=20[=E2=80=A6]I vastly prefer the UFCS version, but unfortunately reduce has=20 its arguments the wrong way around for that if you use the=20 version that takes a seed...In which case the reduce parameter list is wrong, this is a bug and should be fixed. Is there a bug report for this I can connect with? --=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
Sep 25 2015
On Saturday, 26 September 2015 at 06:28:22 UTC, Russel Winder wrote:On Fri, 2015-09-25 at 12:54 +0000, John Colvin via Digitalmars-d-learn wrote:It's been argued about a lot. https://issues.dlang.org/show_bug.cgi?id=8755 https://github.com/D-Programming-Language/phobos/pull/861 https://github.com/D-Programming-Language/phobos/pull/1955 https://github.com/D-Programming-Language/phobos/pull/2033[…]I vastly prefer the UFCS version, but unfortunately reduce has its arguments the wrong way around for that if you use the version that takes a seed...In which case the reduce parameter list is wrong, this is a bug and should be fixed. Is there a bug report for this I can connect with?
Sep 26 2015
On Sat, 2015-09-26 at 10:46 +0000, John Colvin via Digitalmars-d-learn wrote:[=E2=80=A6]I guess the summary is: it's a breaking change, so do it. No we can't do that it's a breaking change.=20 Seems lame given all the other breaking changes that have been. Sad given that reduce is probably the single most important operation in parallel programming.It's been argued about a lot. =20 https://issues.dlang.org/show_bug.cgi?id=3D8755 https://github.com/D-Programming-Language/phobos/pull/861 https://github.com/D-Programming-Language/phobos/pull/1955 https://github.com/D-Programming-Language/phobos/pull/2033--=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
Sep 28 2015
On Monday, 28 September 2015 at 11:04:56 UTC, Russel Winder wrote:On Sat, 2015-09-26 at 10:46 +0000, John Colvin via Digitalmars-d-learn wrote:My thoughts exactly, even though it was partly me that pointed out the breaking changes... I still think we should add fold[lr]? just to fix the ordering.[…]I guess the summary is: it's a breaking change, so do it. No we can't do that it's a breaking change. Seems lame given all the other breaking changes that have been. Sad given that reduce is probably the single most important operation in parallel programming.
Sep 28 2015
Russel Winder via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> On Mon, 2015-09-28 at 11:37 +0000, John Colvin via Digitalmars-d-learn wrote:=20[=E2=80=A6]My thoughts exactly, even though it was partly me that pointed=20 out the breaking changes...Curses, if no-one had pointed out it was breaking maybe no-one would have noticed, and just made the change?I still think we should add fold[lr]? just to fix the ordering.Whatever happens in std.algorithm must also happen in std.parallelism. reduce in std.parallelism was constructed to be in harmony with std.algorithm and not UFCS. --=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
Sep 28 2015
On Friday, 25 September 2015 at 12:51:17 UTC, Russel Winder wrote:
Aha, bingo, spot on. Thanks. Amended now to:
double reduce_string_loop() {
return reduce!"a + 1.0 / (b * b)"(iota(1, 100));
}
double reduce_function_loop() {
return reduce!((t, n) => t + 1.0 / (n * n))(iota(1, 100));
}
which both work as they should. I am sure I will be able to
find a reason why I missed that reduce takes a function of two
parameters not one.
Interesting question on style is whether to use function
application or method call:
reduce!"a + 1.0 / (b * b)"(iota(1, 100))
vs.
iota(1, 100).reduce!"a + 1.0 / (b * b)"
The debate may well turn into a bikeshed one, but it would be
good to know what the opinions are.
The main difference is that "method call" style is more amenable
to chaining (and IMO, it looks cleaner as you don't have nesting
parentheses.
Sep 25 2015
On Fri, 2015-09-25 at 18:45 +0000, Meta via Digitalmars-d-learn wrote:[=E2=80=A6] =20 The main difference is that "method call" style is more amenable=20 to chaining (and IMO, it looks cleaner as you don't have nesting=20 parentheses.I guess coming from Clojure I was less worried about Lisp-style code. I'll try to be more Python/Java/Scala-ish ;-) --=20 Russel. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D Dr Russel Winder t: +44 20 7585 2200 voip: sip:russel.winder ekiga.n= et 41 Buckmaster Road m: +44 7770 465 077 xmpp: russel winder.org.uk London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
Sep 28 2015