Recurrence Relation having undefined variables

2 次查看（过去 30 天）
Dominic Blanco
Dominic Blanco 2021-9-5
编辑： Paul 2021-9-9
Hi there
I am trying to run a recurrence relation from an ODE as doing the calculations by hand is turning out to be long. I am having some trouble doing so. I am getting lots of errors no matter what I try. I feel like this code is correct:
syms lambda c0 c1
for k = 1:1
c(k)
end
function c = c(k)
if k == 0
c = c0;
elseif k ==1
c = c1;
elseif k == 2
c = -lambda * c0/2
else
c = (-c(0) * ((-1)^((k - 1)/2) * (pi/L)^k)/(factorial(k)) - symsum(((-1)^((l - 1)/2) * (pi/L)^l)/(factorial(l)) * c(k+1-l),l,1,k) - lambda * c(k))/((k+2)*(k+1));
end
end
The for loop has k = 1:1 for now just for testing purposes. Eventually I will make it higher. I am getting the following errors:
"unrecognized function or variable 'c1'.
Error in (filename)>c
c = c1;
error in (filename)
c(k)
The issues appear to be with c1, but I don't understand how because I made it symbolic (I do have symbolic math toolbox installed), and I want to keep it as a variable. If I change c1 to a number, now the code starts having issues with lambda! If I make lambda, c0, and c1 all numbers, I get "unrecognized function or variable 'c'."
I am lost! I feel as though this errors should not be happening because I did define these variables. What is going on?

请先登录，再回答此问题。

采纳的回答

Paul
Paul 2021-9-6
Do you get the desired result if you move the line
syms lamda c0 c1
to inside the function?
Also it's kind of confusing to have the output of the functin have the same name as the function itself. Even if it is allowed.
  8 个评论
显示 6更早的评论
Dominic Blanco
Dominic Blanco 2021-9-9
This does indeed work! I was also able to find one mistake in my work done by hand, which was the goal of me writing this. If all but one of the terms matches my handwritten work, I believe this is correct! I did accept your answer as this does answer my question.
If I am to be more picky, is there a way to determine how the output behaves? To explain what I mean, most of the terms in c_5's output have things factored out and fractions written weirdly. Most of the terms have (something/6 /20L. I would love for that to say 120L instead of 6/20L. Not all terms behaves like this, as there is one that has 120 in the denominator, but is there a way to make them all behave the same way? No worries if not, this is still very helpful!
Paul
Paul 2021-9-9
编辑：Paul 2021-9-9
Hi Dominic,
I'm not sure what you mean by the "something/6/20L" in the context of any of the output above. Maybe you're seeing something different in the Matlab command window as compared to how Live Script (which I think is what Answers uses) formats its output? In any case, the Symbolic Math Toolbox offers various functions for simplifying and/or manipulating and/or rewriting expressions (search the doc for "Fomula Manipulation and Simplification"), so I suspect you can get to the form that you want. If still having trouble, post here (or in a new question) and show the specific expression of concern and describe what the desired end product should look like.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Symbolic Math Toolbox 的更多信息

标签

产品


版本

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by