etb's profile - activity

@calc314, this is super helpful. Thanks!

@kcrisman, thank you for the update. Do you have a link to somewhere where I can read about this or could you elaborate what this entails and when such a thing would happen?

This is super helpful! Thanks. Is there a way to limit results to the real space? I looked at wolfram Alpha I can make such assumption explicit using [Simplifyx^2+1=0 Which is different from x^2+1=0, the latter allows fro complex solutions whereas the former doesn't. I trying looking around, but couldn't find a similar option in SM. Do you know where I can learn more about this?

It could be helpful if you posted some reproducible code?

@calc314 thank you for your solution. Is this a math issue or a SageMath, i.e. is this problem due to something mathematical I am not aware of?

@kcrisman, any news in regard to getting hold of the Sage code from interact.sagemath.org? Thanks!

@Masacroso in this regard WolframAlpha might prove to be a bit like MS Word. It's easy at first, but down the road, what at first seemed to be a convenience is now a bug.

Would this give you what you are looking for? (assuming your interval is [-1;2]

f(y) = x^4-3*x+8
f.show()
find_local_maximum(f, -1, 2)

I am generally big on plotting unction like this, you can try to get a feel of your function

plot(f(y), -2,3)

I highly recommend the SageMath Calculus Tutorial if you at all have the time.

Update,

If I run your updated model with your coefficients, e.i.,

f = (1/4)*log(2.02000000000000*x + 1) + (1/2)*log(0.00999999999999979*x + 1) + (1/4)*log(-2*x + 1)
find_local_maximum(diff(f,x), 0, 1)

i get,

(95160969.23167175, 0.50000000262712752)

Could you explain what you expect and why? Did i possibly misinterpret your code? (I did added some parenthesis and some multiplication symbols).

What have you tried? Woudl it be possible for you to post some of your code. Didi you look at this question? Here's some simply code to help you generate a 7 x 7 matrix with some random integers B = matrix(7,7, sample(xrange(100), 49)); B however, I am not sure that this is what you are looking for. If you specific and post code I'll be happy to try to help you!

It would make it easier to understand your problem, and to provide an answer, if you could provide a reproducible example, i.e. enough code to reproduce the equations, complex roots, and converting equations you mention. This would also increase the value of both question and answer for others who might face similar a challenge in the future.

@paulmasson, thank you for your response. I forgot about the Interact part of the Sage wiki. Thanks. I recall I looked at it, but it seemed defunct and not like a living community. We should definitely work to salvage the example from there too.

@kcrisman, The Interact project looks very much like what I imagined. I too hope we can get something similar off the ground again, and hopefully we will be able to deal with the curation. Do you know if it is possible to download the whole site or somehow get access to the Sage code? I can’t seem to get it of the site via Wayback Machine.

direction for how to ask a good question, e.g. aim to post a question with code that can reproduce your problem, make it short.

I am sure most of you are aware of the Wolfram Demonstrations Project. If not, it’s a library of interactive models demonstrating different mathematical concepts. If you buy Mathematica you can edit and experiment with the code yourself. I find it really helpful to be able to investigate something in a interactive graph to understand the relationships in say an economic model, e.g. this example of a basic supply and demand model, this more intricate Keynesian IS-LM Model, or this model that allows you to investigate income and substitution effects with different utility functions.

Friendly people here at ask.sagemath have a couple of times answered my questions by posting code to http://sagecell.sagemath.org, which I really appreciate, e.g. this visualization of logistic population growth, but is there a way to search for SageMath code examples or some library of interactive SageMath models demonstrating different mathematical concepts like the Wolfram Demonstrations Project? I'm also interested to share projects myself.

I think something like a SageMath "Demonstrations Project" could be a great way to demonstrate the power of SageMath in an very accessible way, and possibly contribute to spreading the awareness of SageMath.

@ndomes, how did you create this page http://sagecell.sagemath.org/?q=dgweis do you have an account somewhere or? I am interested to share some sage code online.

I like this explanation on Python Foundation page.

I'm reproducing whats in my math book, or I am trying to. There's a relatively simply equation that I'm supposed to solve, at 8.5 and get 12,14013462. However, when I do this in Sage I get a whole string of complex numbers. I've figured out how to reduce this glory of symbols of numbers into whats in my book, but I feel I am committing some form of atrocity, but maybe my book is simply off? Please let me know if this is not the place for questions like this.

I have this function and _solution_

f(x) = 10.28/(1+3.177*e^(-0.224*x))
fs = solve(f(x)==8.5, x)
show(fs)

However, here is what I get and it's not 12,14 (below is the code I use to cut down the glorious complexity to something that resembles what is in my book),

fs1 = fs[0]  # they seem identical so I take the first item 
fs2 = numerical_approx(fs1.rhs())
fs3 = fs2[0] # simply shaving off the complex number
show(fs3)
type(fs3)

Beautiful. Thanks! @ndomes, would it be possible for you to add your comment as a answer so that I can make it as answered? Thanks.

This is a followup question to this question where @mforets helped me translate some Ti Nspire code to Sagemath code. I now have following,

t = var('t')
y = function('y')(t)
ye = desolve(diff(y,t) == 2*10^(-5)*y*(1500-y), y, ics=[0,50])
ye = ye*3/100
yt = solve(ye.simplify_log(), y)
show(expand(yt))

Now I'm interested to visualize this result, reproducing some lecture notes. I looked at the examples given in the Sage Quickstart for Differential Equations, but I cold not reproduce what was there with my example.

My lecture notes has a lot like this that I'm aim at

By copying the right hand side (code below figure) manually I can get this, but I feel like I'm missing something;

P = plot((1500*e^(3/100*t)/(e^(3/100*t) + 29)),t,0,250, color='red')
L = line([(0,1500), (260,1500)], linestyle=":", color="grey")
show(P+L, figsize=5)

Thanks a lot. I cannot answer your question, but I'll get back to you here if I find an answer to that.