<a>
  <b>
    <c>A</c>
    <d>1</d>
  </b>
  <b>
    <c>B</c>
    <d>2</d>
  </b>
  <b>
    <c>A</c>
    <d>3</d>
  </b>
</a>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
	<xsl:for-each select="/a/b[1]">
 		<sum1><xsl:value-of select="sum(../b[c = /a/b[1]/c]/d) "/></sum1>
 		<sum2><xsl:value-of select="sum(../b[c = ./c]/d)  "/></sum2>
	</xsl:for-each>
</xsl:template>

</xsl:stylesheet>