Although trained as a mathematician and happily married, Sylvia has psychological issues that are interfering with her life. The main focus of this novel is on her interactions with her therapist in which Sylvia's drawings are used to gain access to her repressed memories of child abuse and her connection to a murderer.
Considering that the author has degrees in mathematics from Cambridge University and that the subtitle describes this book as a workl of "mathemafiction", there is surprisingly little to say about math in this book. Math occasionally shows up as representing one side of a dichotomy, with art forming the other branch. Math is presented as being precise, objective and detail oriented. Her training in math and her engineer husband's attitudes represent this side. Both her desire to make a living from art (as opposed to working with computers, which is where her mathematical training led her) and her obsessive drawing of pictures whose subconscious meaning eludes her are on the other side.
(quoted from Infinite Sum)
Art, color, nightmares, and the subconscious; they're all a mystery, filled with possibilities of hope and change. But math is different. Math is real and solid, right or wrong, with no uncertainties. Art plays games, while math follows rules. art soars, and math measures its path. Art takes you where you don't want to go. But math lets you stay unmoving, right where you are.
Measures don't change just because your mind gets distracted. Integers don't shatter and their edges won't cut. They're not sharp. Real numbers don't paint in red and black. And equations never land you in therapy.
There again, equations probably don't land you in art class either. But I'm giving my dreams one final fling before going back to work. I've promised Donald I'll get a job when Adam turns ten; use those hardlearned mathematical skills; sum those graduate letters after my name into a winning resume, though I'm not sure they sum to me.

From my perspective, this is a false dichotomy, or at least a greatly exaggerated one. But, at least this book does not promote the antimath sentiment that I often see in similar works of fiction. Instead, both sides of the dichotomy seem to be appreciated for what they have to offer. In addition, the concept of infinite sums shows up not only in the title but in one final mathematical/religious metaphor at the end.
Apparently this book is a sequel to Divide by Zero featuring the same characters. I have not yet read that one, but I am under the impression that it is even less mathematical than Infinite Sum. I will followup here or with a separate entry for Divide by Zero if I ever read it (or hear from someone has). 