Problem Creating a Function

Hello comunity! I'm trying to create this function, but the problem is that i can't input the straight lines parallel in a period of time! for example y=0.1 between 0 and 0.625 seconds and x=0 between 1 and 0.1 p.u..

Thank you! =)

[Jan]

What does "create this function" exactly mean? Do you want to draw a diagram or create a function, which replies the specific y-value for a provided x-value?

[Nuno]

I want to create a function wich replies the specific y-value for a provided x-value and i could sampling .

Answer 1

[Roger Stafford]

Strictly speaking, you cannot define a (single-valued) function that does what you depict, since it is undefined at t = 0. It is necessary to express your "curve" parametrically. Devise some kind of parameter that changes monotonically throughout the curve's path. For example, define parameter s as advancing just as t does except at t = 0 where we defined s as changing from 0 to 1 while t remains constant at 0. You can easily write a matlab function with two outputs, v and t, that does this. Let s be some vector of s values.

 [v,t] = Nunosfunc(s)
 t1 = (s<0);
 t2 = (0<=s)&(s<1);
 t3 = (1<=s)&(s<1+.625);
 t4 = (1+.625<=s)&(s<1+3);
 t5 = (1+3<=s);
 v = t1.*1.0+t2.*(1.0-(1.0-0.1)*s)+t3.*0.1+...
      t4.*(0.1+(0.9-0.1)/(3-.625)*(s-1-.625))+t5.*0.9;
 t = t1.*s+t2.*0+(t3|t4|t5).*(s-1;
 return

This is very similar to generating points, say, on an ellipse

 x^2/9+y^2/16 = 1

This also cannot be accomplished with a function, but must be generated using some parameter - in this case x = 3*cos(s), y = 4*sin(s), where the parameter s varies over a range of 2*pi.

Note that if in your problem you only wanted to plot that curve, you need only give 'plot' the coordinates of six key (v,t) points, four of them at the bends, using the '-' option and plot will fill in the straight lines for you.

[Nuno]

Thank you! but in my matlab showm this:

Undefined function or variable 's'.

Error in Untitled (line 3) [v, t] = Nunosfunc(s);

[Jan]

I assume, that Roger forgot a "function" and it should be:

function [v,t] = Nunosfunc(s)

Then "s" is the input argument.

[Roger Stafford]

Thanks, Jan. Yes I forgot the 'function' designation. (More senior moments!)

[Nuno]

Error using Nunosfunc (line 2) Not enough input arguments.