how to convert discrete data to continuous data?

Hello I have discrete A,B,C,D system matrices, and i want to convert them in continuous , i have written a script for this but it is giving me error . how should i do this ?

********

load ABCD_matrix.mat
sysd=ss(As,Bs,Cs,Ds);
sysc=d2c(sysd,'zoh');
[Asc,Bsc,Csc,Dsc]=ssdata(sysc);
********************

the error is

Error using DynamicSystem/d2c (line 35)

The first input argument of the "d2c" command must be a discrete-time model.

Error in LQGG (line 5)

sysc=d2c(sysd,'zoh');

Answer 1

[Honglei Chen]

You need to specify the sample time in ss, something like

ss(A,B,C,D,Ts)

[Azzi Abdelmalek]

Aniket, sysd=ss(As,Bs,Cs,Ds) ; is not a discrete model, it's continuous

[Aniket]

ok but if the A,B,C,D matrix data is discrete then how should i convert it to continuous?