How sexy are numbers? Stupid question? Well, Hollywood seems to think the dry-as-chalk-dust-world of quadratic equations can pack an emotional punch.

A Beautiful Mind attempted (and largely failed) to bestow a hipness on extremely long-division and now director John Madden gets his pocket calculator out.

In mathematics, a proof is the successful application of a rigorous set of rules to an unimaginably complex problem to achieve a copper-bottomed solution.

Adapting David Auburn's play, Madden explores a mystery whose key lies somewhere between the certainties of maths and the shifting emotional sands of human nature.

No, it's not sounding very promising…but there's actually more to it than scenes of feverish scribbling down of apparently random numbers and the inevitable "eureka" moment.

Catherine (Paltrow) has devoted her early twenties to looking after her brilliant but psychologically troubled father Robert (Hopkins), a mathematical genius.

When he dies she's got to put up with the arrival of estranged sibling Claire (Davis) - "she's not my friend, she's my sister" - and the romantic attentions of Hal (Gyllenhaal), a former student of her dad.

Dismissed and isolated by his fellow academics, Robert spent his last years pouring out seemingly incoherent ramblings into notebooks.

However, one of these turns out to be a genuine "proof" and incontrovertible evidence he wasn't ga-ga after all. The only trouble is Catherine claims she wrote it.

That this remains so watchable is largely down to excellent performances from Paltrow as the daughter who fears for her own sanity and Davis as the controlling, list-obsessed big sis from New York.

Things are also enlivened by dialogue delivered by characters uncomfortable with straight-talking : Paltrow's impromptu memorial service address to the tweedy profs who shunned her dad is a highlight.

However, it never quite manages to shake off its theatrical roots and is all too often as dry as the arid equations it's attempting to apply to the human heart.

In other words, it doesn't quite add up.

Tim Evans