Compare Two Symbolic Variables

Set symbolic variable m equal to symbolic variable n and test their equality using kroneckerDelta.

syms m n
m = n;
kroneckerDelta(m,n)

ans =
1

kroneckerDelta returns 1 indicating that the inputs are equal.

Compare symbolic variables p and q.

syms p q
kroneckerDelta(p,q)

ans =
kroneckerDelta(p - q, 0)

kroneckerDelta cannot decide if p == q and returns the function call with the undecidable input. Note that kroneckerDelta(p, q) is equal to kroneckerDelta(p - q, 0).

To force a logical result for undecidable inputs, use isAlways. The isAlways function issues a warning and returns logical 0 (false) for undecidable inputs. Set the Unknown option to false to suppress the warning.

isAlways(kroneckerDelta(p, q), 'Unknown', 'false')

ans =
  logical
   0

Compare Symbolic Variable with Zero

Set symbolic variable m to 0 and test m for equality with 0. The kroneckerDelta function errors because it does not accept numeric inputs of type double.

m = 0;
kroneckerDelta(m)

Undefined function 'kroneckerDelta' for input arguments of type 'double'.

Use sym to convert 0 to a symbolic object before assigning it to m. This is because kroneckerDelta only accepts symbolic inputs.

syms m
m = sym(0);
kroneckerDelta(m)

ans =
   1

kroneckerDelta returns 1 indicating that m is equal to 0. Note that kroneckerDelta(m) is equal to kroneckerDelta(m, 0).

Compare Vector of Numbers with Symbolic Variable

Compare a vector of numbers [1 2 3 4] with symbolic variable m. Set m to 3.

V = 1:4
syms m
m = sym(3)
sol = kroneckerDelta(V,m)

V =
     1     2     3     4
m =
3
sol =
[ 0, 0, 1, 0]

kroneckerDelta acts on V element-wise to return a vector, sol, which is the same size as V. The third element of sol is 1 indicating that the third element of V equals m.

Compare Two Matrices

Compare matrices A and B.

Declare matrices A and B.

syms m
A = [m m+1 m+2;m-2 m-1 m]
B = [m m+3 m+2;m-1 m-1 m+1]

A =
[     m, m + 1, m + 2]
[ m - 2, m - 1,     m]
B =
[     m, m + 3, m + 2]
[ m - 1, m - 1, m + 1]

Compare A and B using kroneckerDelta.

sol = kroneckerDelta(A,B)

sol =
[ 1, 0, 1]
[ 0, 1, 0]

kroneckerDelta acts on A and B element-wise to return the matrix sol which is the same size as A and B. The elements of sol that are 1 indicate that the corresponding elements of A and B are equal. The elements of sol that are 0 indicate that the corresponding elements of A and B are not equal.

Use kroneckerDelta in Inputs to Other Functions

kroneckerDelta appears in the output of iztrans.

syms z n
sol = iztrans(1/(z-1), z, n)

sol =
1 - kroneckerDelta(n, 0)

Use this output as input to ztrans to return the initial input expression.

ztrans(sol, n, z)

ans =
z/(z - 1) - 1

Filter Response to Kronecker Delta Input

Use filter to find the response of a filter when the input is the Kronecker Delta function. Convert k to a symbolic vector using sym because kroneckerDelta only accepts symbolic inputs, and convert it back to double using double. Provide arbitrary filter coefficients a and b for simplicity.

b = [0 1 1];
a = [1 -0.5 0.3];
k = -20:20;
x = double(kroneckerDelta(sym(k)));
y = filter(b,a,x);
plot(k,y)