error TS2339: Property 'subset' does not exist on type 'MathType'. Property 'subset' does not exist on type 'number'.

[topazus]

import * as math from "mathjs"
const d = math.matrix([
  [1, 2],
  [3, 4],
])
var res = math.dotPow(d, 2)
console.log(res.subset(math.index(1, 1)))

run js code, get the expected result: print 16

When I put the same js code in ts file

t1.ts file

import * as math from "mathjs"
const d = math.matrix([
  [1, 2],
  [3, 4],
])
var res = math.dotPow(d, 2)
console.log(res.subset(math.index(1, 1)))

and run ts-node t1.ts

,but get the following output errors:

/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/index.ts:843
    return new TSError(diagnosticText, diagnosticCodes, diagnostics);
           ^
TSError: ⨯ Unable to compile TypeScript:
t1.ts:7:17 - error TS2339: Property 'subset' does not exist on type 'MathType'.
  Property 'subset' does not exist on type 'number'.

7 console.log(res.subset(math.index(1, 1)))
                  ~~~~~~

    at createTSError (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/index.ts:843:12)
    at reportTSError (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/index.ts:847:19)
    at getOutput (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/index.ts:1057:36)
    at Object.compile (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/index.ts:1411:41)
    at transformSource (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/esm.ts:400:37)
    at /Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/esm.ts:278:53
    at async addShortCircuitFlag (/Users/felix/.nvm/versions/node/v18.4.0/lib/node_modules/ts-node/src/esm.ts:409:15)
    at async ESMLoader.load (node:internal/modules/esm/loader:431:20)
    at async ESMLoader.moduleProvider (node:internal/modules/esm/loader:350:11)
    at async link (node:internal/modules/esm/module_job:70:21) {
  diagnosticCodes: [ 2339 ]
}

[josdejong]

The reason is that the method .subset() is only available on a Matrix, and the output of math.dotPow is currently not specific enough to know that it res is indeed a Matrix.

Here is the current type definition of dotPow:

mathjs/types/index.d.ts

Line 1085 in ead6228

dotPow(x: MathType, y: MathType): MathType

This definition should be changed similar to most functions (like exp that is right below it):

mathjs/types/index.d.ts

Lines 1093 to 1097 in ead6228

	exp(x: number): number
	exp(x: BigNumber): BigNumber
	exp(x: Complex): Complex
	exp(x: MathArray): MathArray
	exp(x: Matrix): Matrix

Anyone able to improve the type definitions of dotPow and also dotMultiply and dotDivide?

[josdejong]

Fixed now in v11.5.1 via #2890.