Undefined function 'sparse' for input arguments of type 'sym'. (Matlab)

Question

I'm trying to create a sparse matrix that has non-numeric elements.

syms a b c;

i = [1 1 2 2];
j = [1 2 1 2];
s = [a b 3 c];

sparse(i,j,s,2,2)

which returns this error:

Undefined function 'sparse' for input arguments of type 'sym'.

Error in Test2 (line 8)
sparse(i,j,s,2,2)

Additionally, this is not a sparse matrix. A sparse matrix only makes sense if you have many zero elements. You have none. — sco1
– sco1, Commented Feb 8, 2016 at 19:56
There is no such thing as a sparse symbolic matrix in Matlab. You can convert a sparse (numeric) matrix to symbolic but not the other way around. — horchler
– horchler, Commented Feb 8, 2016 at 20:02
Sparse and symbolic very rarely have to be in the same sentence. — Andras Deak -- Слава Україні
– Andras Deak -- Слава Україні, Commented Feb 8, 2016 at 20:02
@AndrasDeak, how about the commonly used sentence: "Although the population is sparse, they can all recite the same highly symbolic poem by heart." — Stewie Griffin
– Stewie Griffin, Commented Feb 8, 2016 at 20:18
@StewieGriffin you're free to flag my comment if its bluntness offends you;) — Andras Deak -- Слава Україні
– Andras Deak -- Слава Україні, Commented Feb 8, 2016 at 20:19

horchler · Accepted Answer · 2016-02-08 20:50:01Z

3

As I stated in the comments, there is no such thing as a sparse symbolic matrix in Matlab. This is stated in the documentation for the third input argument for the form of sparse you're using:

v — Values
scalar | vector | matrix

...

Data Types: double | logical

Matlab's Symbolic Math (and MuPAD) may take advantage of inherent sparsity internally (for storage and computation).

edited Feb 8, 2016 at 20:50

answered Feb 8, 2016 at 20:42

horchler

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Comments

Marc · Accepted Answer · 2016-02-08 20:41:03Z

1

It's pretty simple: Matlab has no function sparse() that takes symbolic variables as arguments. (s is your problem) The only sparse() function takes just numeric elements.

answered Feb 8, 2016 at 20:41

Marc

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Comments

jpfeifer · Accepted Answer · 2017-01-31 11:44:23Z

0

@horchler is correct that more recent versions of Matlab do not support using the sparse command on symbolic matrices. However, older versions of Matlab allowed this (I tried R2011b and it works there). Thus, you may encounter legacy code that produces the above mentioned error. In this case, you may have to remove the sparse commands manually.

answered Jan 31, 2017 at 11:44

jpfeifer

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