Seppo Ilmari Linnainmaa (born 28 September 1945) is a Finnish

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

and

computer scientist A computer scientist is a scientist who specializes in the academic study of computer science. Computer scientists typically work on the theoretical side of computation. Although computer scientists can also focus their work and research on ...

known for creating the modern version of backpropagation.

Biography

He was born in

Pori Pori (; ; ) is a city in Finland and the regional capital of Satakunta. It is located on the west coast of the country, on the Gulf of Bothnia. The population of Pori is approximately , while the Pori sub-region, sub-region has a population of a ...

. He received his MSc in 1970 and introduced a reverse mode of automatic differentiation in his MSc thesis. In 1974 he obtained the first doctorate ever awarded in computer science at the

University of Helsinki The University of Helsinki (, ; UH) is a public university in Helsinki, Finland. The university was founded in Turku in 1640 as the Royal Academy of Åbo under the Swedish Empire, and moved to Helsinki in 1828 under the sponsorship of Alexander ...

. In 1976, he became Assistant Professor. From 1984 to 1985 he was Visiting Professor at the

University of Maryland The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland, United States. Founded in 1856, UMD is the flagship institution of the Univ ...

, USA. From 1986 to 1989 he was Chairman of the Finnish Artificial Intelligence Society. From 1989 to 2007, he was Research Professor at the VTT Technical Research Centre of

Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...

. He retired in 2007.

Backpropagation

Explicit, efficient error backpropagation in arbitrary, discrete, possibly sparsely connected,

neural networks A neural network is a group of interconnected units called neurons that send signals to one another. Neurons can be either Cell (biology), biological cells or signal pathways. While individual neurons are simple, many of them together in a netwo ...

-like networks was first described in Linnainmaa's 1970 master's thesis, albeit without reference to NNs,Jürgen Schmidhuber, (2015)
Who Invented Backpropagation?
/ref> when he introduced the reverse mode of automatic differentiation (AD), in order to efficiently compute the

derivative In mathematics, the derivative is a fundamental tool that quantifies the sensitivity to change of a function's output with respect to its input. The derivative of a function of a single variable at a chosen input value, when it exists, is t ...

of a differentiable composite function that can be represented as a graph, by recursively applying the

chain rule In calculus, the chain rule is a formula that expresses the derivative of the Function composition, composition of two differentiable functions and in terms of the derivatives of and . More precisely, if h=f\circ g is the function such that h ...

to the building blocks of the function. Linnainmaa published it first, following Gerardi Ostrowski who had used it in the context of certain process models in chemical engineering some five years earlier, but didn't publish.

Notes

External links

* {{DEFAULTSORT:Linnainmaa, Seppo Living people 1945 births People from Pori Finnish mathematicians Finnish computer scientists University of Helsinki alumni Academic staff of the University of Helsinki Machine learning researchers