Solving equations with different ranges

4 次查看（过去 30 天）
jack carter
jack carter 2017-8-30
评论： Star Strider 2017-8-31
I need to get the values of P by using different equations under different values of S, as shown in the attached image. I have written codings for the equations but could someone please guide me on how can I make the equations work along with the given different range of S?
sigma0=5; Lf=12; S=0:0.01:600; S0=0.18; %arbitrary values
P=sigma0*[2*sqrt(S/S0)-(S/S0)]; %Run this eq. for S=<S0 (S is less than & equal to S0)
P=sigma0*(1-2*S/Lf)^2; %Run this eq. for S0<=S<=Lf/2
P=0; %Run this eq. for S>=Lf/2
The value of S0 will be a constant value which I will get by solving another set of equation (not included in this query). All of the values I have taken are arbitrary. Later I will be plotting the resultant values of P and for corresponding values of S.
Thank you
  1 个评论
jack carter
jack carter 2017-8-30
Please add one more detail to this question that later in my function I will be needed to use values of P, from both equations, separately. Like, using the resultant values of equation one (when delta (S) is less than delta0 (S0)) and multiply or add to other parameters. And also using the resultant values of P for second equation and third equation separately with some other parameters. These values will be like my input values to solve other equations. How could I use them separately later on?

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2017-8-30
Using ‘logical vectors’, ‘P’ is not defined for ‘S’ greater than or equal to ‘Lf/2’, so an explicit condition for that region to be 0 is not necessary in the expression.
This seems to me to do what you want:
sigma0=5; Lf=12; S=0:0.01:600; S0=0.18; %arbitrary values
P = @(S,S0,Lf,sigma0) sigma0*((2*sqrt(S/S0)-(S/S0)).*(S<=S0) + ((1-2*S/Lf).^2).*((S0<=S) & (S<=Lf/2)));
figure(1)
plot(S, P(S,S0))
grid
xlabel('S')
ylabel('P')
axis([0 10 ylim])
This uses an anonymous function implementation of your conditional expression.
  9 个评论
显示 7更早的评论
jack carter
jack carter 2017-8-31
编辑：jack carter 2017-8-31
@Star Strider - I am not sure what I am doing wrong. I am a beginner in MATLAB. As per my understanding the variables are already existed in the workspace when I run these codes. I am able to print all of the variables with fprintf command. I have attached the coding file if you could take a look. In the command window is it like I shall type checkranges and it should work? It is working like this for printing the values of all the variables except P.
Star Strider
Star Strider 2017-8-31
The way I wrote my function, you have to supply all the input arguments. It does not automatically take any arguments from your workspace.
This works:
sigma0=5; Lf=12; S=0:0.01:600; S0=130; %arbitrary values
P = @(S,S0,Lf,sigma0) sigma0*((2*sqrt(S/S0)-(S/S0)).*(S<=S0) + ((1-2*S/Lf).^2).*((S0<=S) & (S<=Lf/2)));
figure(1)
plot(S, P(S,S0,Lf,sigma0))
grid
xlabel('S')
ylabel('P')
axis([0 10 ylim])

请先登录，再进行评论。

更多回答（1 个）

Walter Roberson
Walter Roberson 2017-8-30
If you have the symbolic toolbox, you could code in terms of piecewise()

类别

在 Help Center 和 File Exchange 中查找有关 Get Started with MATLAB 的更多信息

标签

产品

Community Treasure Hunt

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

Start Hunting!

Translated by