isstable

Determine whether filter is stable

Syntax

flag = isstable(b,a) flag = isstable(sos) flag = isstable(d) flag = isstable(h)

Description

flag= isstable(b,a)returns a logical output,flag, equal totrueif the filter specified by numerator coefficients,b, and denominator coefficients,a, is a stable filter. If the poles lie on or outside the circle,isstablereturnsfalse. If the poles are inside the circle,isstablereturnstrue.

flag= isstable(sos)returnstrueif the filter specified by second order sections matrix,sos, is stable.sosis aK-by-6 matrix, where the number of sections,K, must be greater than or equal to 2. Each row ofsoscorresponds to the coefficients of a second order (biquad) filter. Theith row of thesosmatrix corresponds to[bi(1) bi(2) bi(3) ai(1) ai(2) ai(3)].

flag= isstable(d)returnstrueif the digital filter,d, is stable. Usedesignfiltto generatedbased on frequency-response specifications.

Details for Fixed-Point Arithmetic

System Object State	Coefficient Data Type	Rule
Unlocked	`'Same as input'`	The function assumes that the coefficient data type is signed, 16 bit, and autoscaled. The function performs fixed-point analysis based on this assumption.
Unlocked	`'Custom'`	The function performs fixed-point analysis based on the setting of the`CustomCoefficientsDataType`property.
Locked	`'Same as input'`	When the input data type is`'double'`or`'fixed'`, the function assumes that the coefficient data type is signed, 16-bit, and autoscaled. The function performs fixed-point analysis based on this assumption.
Locked	`'Custom'`	The function performs fixed-point analysis based on the setting of the`CustomCoefficientsDataType`property.

flag= isstable(h)returnstrueif thedfiltfilter objecthis stable.

Examples

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Filter Stability

Open Live Script

Design a sixth-order Butterworth highpass IIR filter using second order sections. Specify a normalized 3-dB frequency of 0.7. Determine if the filter is stable.

[z,p,k] = butter(6,0.7,'high'); SOS = zp2sos(z,p,k); flag = isstable(SOS)

flag =logical1

zplane(z,p)

Redesign the filter usingdesignfiltand check it for stability.

d = designfilt('highpassiir','DesignMethod','butter','FilterOrder',6,...'HalfPowerFrequency',0.7); dflg = isstable(d)

dflg =logical1

zplane(d)

Create a filter and determine its stability at double and single precision.

b = [1 -0.5]; a = [1 -0.999999999]; act_flag1 = isstable(b,a)

act_flag1 =logical1

act_flag2 = isstable(single(b),single(a))

act_flag2 =logical0

isstable

Syntax

Description

Examples

Filter Stability

See Also

Introduced in R2013a

Signal Processing Toolbox Documentation

金宝app

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