El lunes, 24 de marzo de 2014 17:55:39 UTC-6, Jacob Quinn escribió:
>
> How about
>
> In [186]: @time rand(-1:2:1,10000,10000);
> elapsed time: 2.29940616 seconds (800000224 bytes allocated)
>
> No need for an extra function. This uses a range from -1 to 1 with a step
> size of 2 so you only get those two numbers
>
OK, thanks, I didn't know you could do that. It's still twice as slow as
elementwise_random_block though
(the idea being that it's faster to generate random numbers in a block and
store them than generate them one by one); see below.
I also did not specify correctly that I will also need to generate the
numbers with different probabilities (not necesarily 50--50).
Surprisingly, `elementwise` is sometimes fast (0.8 seconds) and sometimes
slow (5 seconds)...
julia> function using_rand(L)
rand(-1:2:1, L, L)
end
using_rand (generic function with 1 method)
julia> L = 10000
10000
julia> @time rand_pm1_matrix(L);
elapsed time: 1.02277517 seconds (1812500448 bytes allocated)
julia> @time elementwise(L);
elapsed time: 5.062444454 seconds (100000176 bytes allocated)
julia> @time elementwise_random_block(L);
elapsed time: 0.86818943 seconds (900000288 bytes allocated)
julia> @time using_rand(L);
elapsed time: 1.939470921 seconds (800000160 bytes allocated)
>
> On Mon, Mar 24, 2014 at 7:21 PM, David P. Sanders
> <[email protected]<javascript:>
> > wrote:
>
>> Hi,
>>
>> What is the fastest way to create a matrix containing random integers: 1
>> or -1 with equal probability?
>> I have tried the following options but was wondering if I am missing
>> something.
>> (I also need 1, 0 or -1 with different probabilities later, which is why
>> I don't just use a boolean random matrix.)
>>
>> Thanks,
>> David.
>>
>> julia> function rand_pm1_matrix(L)
>> matrix::Array{Int8, 2} = 2 .* randbool(L,L) .- 1
>> end
>> rand_pm1_matrix (generic function with 1 method)
>>
>> julia> function elementwise(L)
>> A = Array(Int8, (L, L))
>> for i in 1:length(A)
>> if rand() < 0.5
>> A[i] = -1
>> else
>> A[i] = 1
>> end
>> end
>> A
>> end
>> elementwise (generic function with 1 method)
>>
>> julia> function elementwise_random_block(L)
>> r = rand(L, L)
>> A = Array(Int8, (L, L))
>> for i in 1:length(A)
>> if r[i] < 0.5
>> A[i] = -1
>> else
>> A[i] = 1
>> end
>> end
>> A
>> end
>> elementwise_random_block (generic function with 1 method)
>>
>> julia> L = 10
>> 10
>>
>> julia> rand_pm1_matrix(L);
>>
>> julia> elementwise(L);
>>
>> julia> elementwise_random_block(L);
>>
>> julia>
>>
>> julia> L = 100
>> 100
>>
>> julia> @time rand_pm1_matrix(L);
>> elapsed time: 6.5661e-5 seconds (188588 bytes allocated)
>>
>> julia> @time elementwise(L);
>> elapsed time: 0.001172332 seconds (10160 bytes allocated)
>>
>> julia> @time elementwise_random_block(L);
>> elapsed time: 0.000131455 seconds (90240 bytes allocated)
>>
>> julia>
>>
>> julia> L = 1000
>> 1000
>>
>> julia> @time rand_pm1_matrix(L);
>> elapsed time: 0.013428217 seconds (18125456 bytes allocated)
>>
>> julia> @time elementwise(L);
>> elapsed time: 0.074257183 seconds (1000176 bytes allocated)
>>
>> julia> @time elementwise_random_block(L);
>> elapsed time: 0.007721683 seconds (9000288 bytes allocated)
>>
>> julia>
>>
>> julia> L = 10000
>> 10000
>>
>> julia> @time rand_pm1_matrix(L);
>> elapsed time: 2.75006866 seconds (1812500448 bytes allocated)
>>
>> julia> @time elementwise(L);
>> elapsed time: 6.727148454 seconds (100000176 bytes allocated)
>>
>> julia> @time elementwise_random_block(L);
>> elapsed time: 2.819847794 seconds (900000288 bytes allocated)
>>
>> \
>>
>
>
