Thanks, it worked!
Em domingo, 4 de maio de 2014 19h06min47s UTC-3, Tony Kelman escreveu:
>
> On the lines where you initialize k and l to [0 0 0 0 0 0], that is an
> array of integers by default. Then in the for loops where you try to assign
> a floating-point result into that array, you get an InexactError because a
> general floating-point number can't be exactly represented as an integer.
> If you change those to float64([0 0 0 0 0 0]) or Float64[0 0 0 0 0 0] or
> [0.0 0.0 0.0 0.0 0.0 0.0], and likewise with t0, v0, and w0, it should work.
>
>
> On Sunday, May 4, 2014 2:40:17 PM UTC-7, Paulo Castro wrote:
>>
>> I was trying to port a function from a previous Python code of mine, and
>> ended with this:
>>
>> # Rubge-Kutta-Fehlberg
>> function RKF45(f, g, h, t0, tf, v0, w0)
>> # Initial values
>> t = t0
>> v5 = v4 = v = v0
>> w = w0
>>
>> tolerance = 10^(-5.0)
>>
>> # Create list for future plots
>> t_list = [t]
>> v_list = [v]
>> w_list = [w]
>>
>> # Values for a, b and c (as on Butcher's tableau)
>> a = [ 0 0 0 0 0 0;
>> 1/4 0 0 0 0 0;
>> 3/32 9/32 0 0 0 0;
>> 1932/2197 -7200/2197 7296/2197 0 0 0;
>> 439/216 -8 3680/513 -845/4104 0 0;
>> -8/27 2 -3544/2565 1859/4104 -11/40 0]
>>
>> b = [16/135 0 6656/12825 28561/56430 -9/50 2/55;
>> 25/216 0 1408/2565 2197/4104 -1/5 0]
>>
>> c = [0 1/4 3/8 12/13 1 1/2]
>>
>> # Relative to y
>> k = [0 0 0 0 0 0]
>>
>> # Relative to z
>> l = [0 0 0 0 0 0]
>>
>> # Compute the next terms
>> for i in t0:h:tf
>> # Compute the next values of K and L
>> for j in 1:6
>> k[j] = f(t + c[j] * h, v + (a[j,:] * k')[1], w + (a[j,:] * l'
>> )[1])*h
>> l[j] = g(t + c[j] * h, v + (a[j,:] * k')[1], w + (a[j,:] * l'
>> )[1])*h
>> end
>>
>>
>>
>> ############################################################################
>> # Compute the next value of V
>> #
>> # Here we implemented a tolerance test
>> #
>>
>> ############################################################################
>> v4 = v + (b[2] * k')[1]
>> #
>> v5 = v + (b[1] * k')[1]
>> #
>>
>> #
>> error = abs(v5 - v4)
>> #
>> if error > tolerance
>> #
>>
>> #
>> h = 0.9 * h * ((tolerance/error) ^ (0.25))
>> #
>>
>> #
>> for j in 1:6
>> #
>> k[j] = f(t + c[j] * h, v + (a[j] * k')[1], w + (a[j] * l'
>> )[1])*h #
>> l[j] = g(t + c[j] * h, v + (a[j] * k')[1], w + (a[j] * l'
>> )[1])*h #
>> end
>> #
>>
>> #
>> v5 = v + (b[1,:] * k')[1]
>> #
>> end
>> #
>>
>> #
>> v = v5
>> #
>>
>> ############################################################################
>>
>> # Compute T and W with the right values of H and L, obtained
>> after the tolerance test
>> t += h
>> w += (b[1,:] * l')[1]
>>
>> # Append new values to the lists
>> push!(t_list,t)
>> push!(v_list,v)
>> push!(w_list,w)
>> end
>>
>> return t_list, v_list, w_list
>> end
>>
>> After running this code, I got a mysterious error message:
>>
>>
>>
>> *ERROR: InexactError() in setindex! at array.jl:346while loading
>> /home/paulo/Documents/Working/ex1.jl, in expression starting on line 28*
>>
>> ex1.jl is the file I used to test my function:
>>
>> include("rungekutta.jl")
>>
>> function f(t, v, w)
>> return (v*(v-a)*(1-v) - w + I)/ε
>> end
>>
>> function g(t, v, w)
>> return (v - p*w - b)
>> end
>>
>> ε = 0.005
>> a = 0.5
>> b = 0.15
>> p = 1.0
>> I = 0.0
>> h = 0.005
>>
>> # Initial and final values of time
>> t0 = 0
>> tf = 8
>>
>> t, v, w = RKF45(f, g, h, t0, tf, 0, 0) # v0 = w0 = 0
>>
>> Can someone help me with finding what's the problem? I tried a lot of
>> things, but always end with this error.
>>
>> Thanks!
>>
>>
