Cognomen Alagaratnam (Alagaratnam 
) , all over the world, is a rare surname. The family name Alagaratnam is habitual in Bermuda, where it is quite a rare surname, Sri Lanka, and Malaysia, where it is a rare surname. In absolute terms, it is the most numerous in Sri Lanka, Malaysia, and Australia. Also, Alagaratnam is the forename as well as the last name.
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| Alagaratnam | Australia, Malaysia, Canada, Sri Lanka, United Kingdom |
| w. t. i. alagaratnam Ceylon Tamil civil engineer (b. 1895) |
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| jasmini alagaratnam researcher (ORCID 0000-0003-2256-423X) |
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| swethan alagaratnam researcher |
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| rathy alagaratnam candidate in United Kingdom General Election |
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| sharmini alagaratnam researcher |
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| suhan alagaratnam cricketer, MY (b. 1986) |
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