Error: 'When calling a function, or indexing a variable, use parentheses. Otherwise check for mismatched delimiters.'

Hi! I am trying to define a new function type (ft) which I was later use to fit a curve. The code I have written is as follows, and I keep receiving the same error message. Can anyone help?

ft = ( 'b + (a * ((x+k)*(x^-1)) )', 'independent', 'x', 'coefficients', {'a', 'b', 'k'} )

I have tried various different types of the equation, with different parentheses including:

parentheses around the whole equation at start as well as parenthese around full function

and 'b + (a*(x/(x+k)))'

[Dyuman Joshi]

It's not clear as to what you want to do with the particular code.

Do you wish to use a function? or do you wish to resolve the equation in some manner?

[Cara]

I am trying to define a new function type, which I will then use later to fit a curve

[Dyuman Joshi]

So you want plot a graph corresponding to a, b and k as constants/coefficients and x as the independent variable?

[Cara]

yes, however the line of code I am looking at is just to define the fittype custom equation.

I would then do f = (x, y, ft, 'StartPoint', 'a0, b0, k0') (a0, b0, k0 are predefined variables)

and then plot (x, y, f, 's')

to generate a graph of the original data with the fit curve according to my predefined equation.

Answer 1

[the cyclist]

Is this what you are trying to do?

ft = fittype( 'b + (a * ((x+k)*(x^-1)) )', 'independent', 'x', 'coefficients', {'a', 'b', 'k'} )

ft = 
     General model:
     ft(a,b,k,x) = b + (a * ((x+k)*(x^-1)) )