Blocks That Linearize to Zero
A common cause of linearization issues is a block that unexpectedly linearizes to a gain of
zero. To diagnose the cause of a zero block linearization, you can consider:
- Any corresponding diagnostic messages. These messages can highlight common
causes of zero linearizations and propose potential solutions. - The block operating point; that is the values of the block states and inputs at the
model operating point used for linearization. For example, if the input to a saturation
block is outside the block saturation limits, and the block is not configured to linearize
as a gain, the block linearizes to zero. - The block parameters. For example, if a block is configured to use nondouble inputs or
states and is linearized using numerical perturbation, it linearizes to zero.
A zero block linearization does not necessarily indicate a linearization problem; that is,
you may expect a block to linearize to zero under the expected operating conditions of the
model. For example, if a Trigonometric Fcn block is configured as a sin function and the
input value is π/2 at the model operating point, then the block linearizes to zero.
Blocks with Substituted Linearizations
Errors in defining a custom block linearization can be difficult to diagnose. After fixing
issues related to diagnostic messages and zero linearizations, if your model still does not
linearize as expected, verify that any substituted block linearizations in your model are
correct.
For more information on specifying substitute block linearizations, see “When to Specify
Individual Block Linearization” on page 2-161.
Find Specific Blocks in Linearization Results
If your model still does not linearize as you expect after fixing linearization issues related
to potentially problematic blocks, you can query the Linearization Advisor for additional
block diagnostic information. You can gain insight into your model linearization using this
information. For example, you can investigate:
- Blocks that are linearized using numerical perturbation.
- Sampling rates of block linearizations in multirate models by finding blocks with a
specified sample time.
Identify and Fix Common Linearization Issues