chgTimeUnit

Change time units of dynamic system

Syntax

sys_new = chgTimeUnit(sys,newtimeunits)

Description

sys_new = chgTimeUnit(sys,newtimeunits) changes the time units of sys to newtimeunits without modifying system behavior. The time- and frequency-domain characteristics of sys and sys_new match.

Examples

Change Time Units of Dynamic System Model

Create a transfer function model.

num = [4 2];
den = [1 3 10];
sys = tf(num,den);

By default, the time unit of sys is 'seconds'. Create a new model with the time units changed to minutes.

sys1 = chgTimeUnit(sys,'minutes');

This command sets the TimeUnit property of sys1 to 'minutes', without changing the dynamics. To confirm that the dynamics are unchanged, compare the step responses of sys and sys1.

stepplot(sys,'r',sys1,'y--');
legend('sys','sys1');

The step responses are the same.

If you change the TimeUnit property of the system instead of using chgTimeUnit, the dynamics of the system do change. To see this, change the TimeUnit property of a copy of sys and compare the step response with the original system.

sys2 = sys;
sys2.TimeUnit = 'minutes';
stepplot(sys,'r',sys2,'gx'); 
legend('sys','sys2');

The step responses of sys and sys2 do not match. For example, the original rise time of 0.04 seconds changes to 0.04 minutes.

Input Arguments

sys — Dynamic system model

dynamic system model

Dynamic system model, specified as either an identified LTI model or identified nonlinear model. For information regarding specific model types see Dynamic System Models.

newtimeunits — New units of time

'seconds' (default) | 'nanoseconds' | 'microseconds' | 'milliseconds' | 'minutes' | 'hours' | 'days' | 'weeks' | 'months' | 'years'

New time units, specified as one of the following values:

• 'nanoseconds'

• 'microseconds'

• 'milliseconds'

• 'seconds'

• 'minutes'

• 'hours'

• 'days'

• 'weeks'

• 'months'

• 'years'

Output Arguments

sys_new — Dynamic system model

dynamic system model

Dynamic system model of the same type as sys. The time response of sys_new is the same as sys. For identified linear models both the model parameters and their minimum and maximum bounds are scaled to the new time units.

Version History

Introduced in R2012a