Well, I'm not sure what the intention was, but this fact is true: for
floating-point values x and y of the same type, x == y is true if and only
if string(x) == string(y).
On Wed, Nov 5, 2014 at 5:36 AM, Steven G. Johnson stevenj@gmail.com
wrote:
On Tuesday, November 4, 2014 8:44:55 PM
On Wed, Nov 5, 2014 at 2:48 AM, Jameson Nash vtjn...@gmail.com wrote:
fun fact: even with format long, matlab doesn't always print enough
digits to reconstruct the number
Do you have an example? If true, this is rather horrifying. Is there simply
no way to print a true value from Matlab then?
The matlab docs clearly specifies format long as 15 digits
http://www.mathworks.se/help/matlab/matlab_prog/display-format-for-numeric-values.html.
Julia usually prints 16 (or 17) digits for a call to rand().
This is a typical distribution of the number of digits from a
`rand(1_000_000)` call
You may want to check the isapprox function.
IMO simulation is not necessary here --- double float is known to have
52 bits for the significand, so which tranlates to a bit less than 16
decimal digits, + 1 for rounding error (magnitude of rounding error is
non-uniform when reading back from decimal), which is how you get 17, so
clearly 15 is
I couldn't resist this after my cholfact() revelation...
On Wednesday, November 5, 2014 11:23:03 AM UTC+1, Stefan Karpinski wrote:
Well, I'm not sure what the intention was, but this fact is true: for
floating-point values x and y of the same type, x == y is true if and only
if string(x) ==
This code prints a random Float64 that requires more than 15 digits to
reconstruct:
while true
x = rand()
if parsefloat(@sprintf(%.15f, x)) != x
println(x)
break
end
end
There are lots of them. What's more surprising is that if you replace 15
with anything up to 20,
On Wednesday, November 5, 2014 4:25:16 AM UTC-6, Stefan Karpinski wrote:
On Wed, Nov 5, 2014 at 2:48 AM, Jameson Nash vtjn...@gmail.com wrote:
fun fact: even with format long, matlab doesn't always print enough
digits to reconstruct the number
Do you have an example? If true, this is
I think that you are just running floats which are subnormal in a
fixed-point decimal representation: with %.17f, they have (on average)
a single 0 after the decimal dot, with %.18f, they have two,
etc. Printing them with %f but a fixed number of digits is not the right
way, since you waste digits
No, these aren't subnormal values, although they are small. Using %.16e
does print them all accurately though, so that's a bit misleading. By
hang I meant that it doesn't return quickly, not that it won't ever
return.
On Wed, Nov 5, 2014 at 2:27 PM, Tamas Papp tkp...@gmail.com wrote:
I think
julia f(x::Float64, y::Float64) = 2x + y;
julia f(10.97,23.9985)
45.9385005
The above method execution of function f returns an answer that I cannot
understand. Can someone clarify?
Thank you.
Hi Neil,
Julie does math the same way that all computers do math. You're probably coming
from another language where a lot of effort is invested into pretending that
computers offer a closer approximation to abstract mathematics than they
actually do. Those systems have been lying to you.
Put
Thanks
On Tuesday, November 4, 2014 2:13:37 PM UTC-5, John Myles White wrote:
Hi Neil,
Julie does math the same way that all computers do math. You're probably
coming from another language where a lot of effort is invested into
pretending that computers offer a closer approximation to
Some systems round their answers as John said but it's easy to check that
it's a lie:
R version 3.1.0 (2014-04-10) -- Spring Dance
2*10.97 + 23.9985
[1] 45.9385
2*10.97 + 23.9985 == 45.9385
[1] FALSE
This is perl 5, version 16, subversion 2 (v5.16.2)
DB1 x 2*10.97 + 23.9985
0 45.9385
DB2
On Matlab R2013b:
2*10.97 + 23.9985
ans =
45.9385
2*10.97 + 23.9985 == 45.9385
ans =
0
-- mb
On Tue, Nov 4, 2014 at 7:48 PM, Stefan Karpinski ste...@karpinski.org
wrote:
Some systems round their answers as John said but it's easy to check that
it's a lie:
R version 3.1.0
julia 2*10.97 + 23.9985
45.9385005
julia 2*10.97 + 23.9985 == 45.9385005
true
Amazing. I never expected this. Is floating point comparison going to
be guaranteed?
On 2014年11月05日 08:48, Stefan Karpinski wrote:
Some systems round their answers as John said but it's easy to
On Wed, Nov 5, 2014 at 2:06 AM, K Leo cnbiz...@gmail.com wrote:
julia 2*10.97 + 23.9985
45.9385005
julia 2*10.97 + 23.9985 == 45.9385005
true
Amazing. I never expected this. Is floating point comparison going to be
guaranteed?
What's shocking about this? What do you
Don't know what you mean by guaranteeing a floating point comparison.
In any event, you should never check equality when comparing floating
point numbers (except perhaps in special cases). Instead, use a
tolerance:
tol = 1e-12;
if (abs(a-b) tol)
# Close enough
else
# not equal
end
The
Just to follow up on this topic, here's what Matlab does:
2*10.97 + 23.9985
ans =
45.9385
2*10.97 + 23.9985 == 45.9385
ans =
0
format long
2*10.97 + 23.9985
ans =
45.9385005
2*10.97 + 23.9985 == 45.9385005
ans =
1
Note that Matlab's display
I meant this: to check whether 2 floating point valuables equal I had
always had to do something like abs(x-y)1.e-5 (never simply x==y) in
other languages. I wonder whether checking x==y would be sufficient in
Julia?
On 2014年11月05日 09:30, Stefan Karpinski wrote:
On Wed, Nov 5, 2014 at 2:06
The == check works exactly the same way in Julia as it does in other
languages. It's the printing of the numbers that's more precise.
On Wed, Nov 5, 2014 at 2:41 AM, K Leo cnbiz...@gmail.com wrote:
I meant this: to check whether 2 floating point valuables equal I had
always had to do something
On Tuesday, November 4, 2014 8:42:02 PM UTC-5, K leo wrote:
I meant this: to check whether 2 floating point valuables equal I had
always had to do something like abs(x-y)1.e-5 (never simply x==y) in
other languages. I wonder whether checking x==y would be sufficient in
Julia?
It
On Tuesday, November 4, 2014 8:44:55 PM UTC-5, Stefan Karpinski wrote:
The == check works exactly the same way in Julia as it does in other
languages. It's the printing of the numbers that's more precise.
Maybe K. Leo was asking whether Julia always prints out enough decimal
digits from
23 matches
Mail list logo
